No future fruition mention in the text. All past tense.
Although "has entered" His rest and "has himself also rested" from his works (Hebrews 4:10) is past tense, just like "have been" saved through faith (Ephesians 2:8) and "have been" justified by faith (Romans 5:1) is past tense "with ongoing present results," it's full fruition is yet future, when believers receive their glorified bodies. (Romans 8:23, 30)
And once again two things mention in verse ten. The Rest which is the Gospel and the Sabbath keeping which God participated in. Also the ceasing of work is in addition to the Rest before mention. Something else that needs attention is the fact that the ceasing from work is "as God did".
The word "Gospel" is not found in Hebrews 10, but in Hebrews 4 and keeping the Sabbath day under the law is not the Gospel. The Gospel is the "good news" of the death, burial and resurrection of Christ (1 Corinthians 15:1-4) and is the
power of God unto salvation to everyone that
BELIEVES.. (Romans 1:16) To "believe" the Gospel is to
trust in the death, burial and resurrection of Christ as the ALL-sufficient means of their salvation.
*Only those who truly BELIEVE the Gospel enter this (sabbatismos rest) in Hebrews 4:9,10. Those who don't truly believe the gospel, but a "different" gospel do not enter. (2 Corinthians 4:3,4; Galatians 1:6-9; Hebrews 4:2-3) The Gospel is a message of grace to be received through faith. The Gospel is not a set of rituals to perform, a code of laws to be obeyed or a check list of good works to accomplish as a prerequisite for salvation. The Gospel is NOT salvation by grace plus law, faith plus works.
Only one mention of God ceasing from work in the Bible and that is at the completion of Creation. It was a Physical ceasing from physical work. There remaineth therefore a rest to the people of God. For he that is entered (past tense) into his rest, he also (in addition) hath ceased (past tense) from his own works, as (just like) God did from his. (Heb 4:9-10 KJV)
W E Vine mentions ...sabbatismos (σαββατισμός), “a Sabbath-keeping,” is used in Heb 4:9, rv, “a sabbath rest,” kjv marg., “a keeping of a sabbath” (akin to sabbatizo, “to keep the Sabbath,” used, e.g., in Ex 16:30, not in the NT);
here the sabbath-keeping is the perpetual sabbath “rest” to be enjoyed uninterruptedly by believers in their fellowship with the Father and the Son, in contrast to the weekly Sabbath under the Law. Because this sabbath “rest” is the “rest” of God Himself, He 4:10,
its full fruition is yet future, though believers now enter into it. In whatever way they enter into divine “rest,”
that which they enjoy is involved in an indissoluble relation with God. (Vine's Expository Dictionary of New Testament Words)
*Notice that Hebrews 4:9 uses the word sabbatismos (Sabbath rest) rather than sabbaton (Sabbath day).
Sabbatismos is only used once in the Bible. Had the writer of Hebrews desired to emphasize the seventh day for sacred worship, the word sabbaton would have been used. Don't confuse the shadow with the reality. The one who has entered (past tense) His rest has himself also rested (past tense) from his works. Vine in his collected writings adds this note...
There remains therefore a sabbath rest [a sabbatismos, or sabbath-keeping] for the people of God.—no sooner had His handiwork been marred by sin than God began to work with a view to
man’s redemption and to the restoration of the enjoyment of the rest of communion with Him. Hence all the pre-figurative sacrifices and types and shadows in the Old Testament. The work of redemption having been accomplished on the Cross, God raised Him from the dead, seated Him at His right hand and rested once more.
Man was now called not to keep a seventh-day rest, appertaining to the old creation,
but an abiding rest in Christ. In Him God rests eternally. The believer is called to apprehend what it means to enjoy His rest; and this as against the world, the flesh and the devil.
This is granted not one day in the week,
but a sabbatismos, a sabbath-keeping all the days of the year. This word sabbatismos has a Greek suffix added to a Hebrew word. This is used instead of katapausis (as in He 3:11, 18; 4:1, 3, 5, 10, 11), a cessation....
...As has been pointed out, our sabbath in this day of the indwelling Holy Spirit and His ministry, is not one day in the week; “there remains [i.e., abides continually] a sabbath rest [a sabbatismos, a sabbath-keeping] for the people of God.” Our rest is in the living and glorified Christ on the ground of His finished work at Calvary.
This rest does not depend on special days, it is not intermittent.
Context says the rest is the Gospel.
Not the context of Hebrews 4:9,10. You need to go to Hebrews chapter 4 to find the word "Gospel." The rest is "sabbatismos." The Gospel is the "good news" of the death, burial and resurrection of Christ. (1 Corinthians 15:1-4) Although for centuries the Jews had found their physical rest in a day, the New Covenant takes the focus off the shadows of the Old Testament signs and rituals and reveals their spiritual substance --
the fulfillment/reality—in the person of Jesus Christ. (Colossians 2:16-17) Christians find complete Sabbath "sabbatismos" rest in Christ's finished work on the cross. The New Testament Sabbath rest is entered into by ceasing from one’s "works" of trying to earn salvation though keeping the Law.
But Christ as a son over his own house; whose house are we (By a new and living way (which is the rest, the Gospel), which he hath consecrated for us, through the veil, that is to say, his flesh; And having an high priest over the house of God. Heb 10:20,21) if we hold fast the confidence and the rejoicing of the hope firm unto the end.
(Heb 3:6 KJV)
For we are made partakers of Christ ( through the veil, that is to say, his flesh (which is the rest, the Gospel); And having an high priest over the house of God) if we hold the beginning of our confidence stedfast unto the end;
(Heb 3:14 KJV)
Let us therefore fear, lest, a promise being left us of entering into his rest (partakers of Christ through the veil, that is to say, his flesh (which is the rest, the Gospel; And having an high priest over the house of God), any of you should seem to come short of it. For unto us was the GOSPEL preached, as well as unto them: but the word preached did not profit them, not being mixed with faith in them that heard it.
(Heb 4:1- KJV)
Once again, the Gospel is the "good news" of the death, burial and resurrection of Christ (1 Corinthians 15:1-4) and is the
power of God unto salvation to everyone that
BELIEVES.. (Romans 1:16) Those who truly believe the Gospel have entered His rest. In regards to Hebrews 3:6-14, in verse 8, we read - Do not harden your hearts as in the rebellion, in the day of trial in the wilderness, 9 Where your fathers tested Me, tried Me, And saw My works forty years. 10 Therefore I was angry with that generation, And said,
'They always go astray in their heart, And they have not known My ways.' Verses 18-19 - And to whom did He swear that they
would not enter His rest, but to those who
did not obey? So we see that they could not enter in because of
unbelief. In Jude 1:5, we read - The Lord delivered His people (the Israelites) out of Egypt, but later
destroyed those who did not believe.
In Hebrews 3:14, we read: For we
have become [past tense Gk. verb, gegonamen, meaning we have become already] partakers of Christ if we hold the beginning of our confidence steadfast to the end. The wording of this verse is not - "and you will be saved (future indicative) if you (future indicative) hold fast." It is rather -
"you have been, and now are, really saved, if in the future you hold fast." Future perseverance would be proof of genuine conversion. Not holding our confidence steadfast to the end indicates a flaw in our confidence from the start. Anyone can "profess" to have confidence and to be a partaker of Christ, but failing to hold that confidence stedfast unto the end proves otherwise.
In Hebrews 4:2-3, we read: For indeed the gospel was preached to
US as well as to
THEM; but the word which
THEY heard
did not profit them, not being mixed with faith in those who heard it. For
WE who have BELIEVED do enter that rest, as He has said: "So I swore in My wrath, 'They shall not enter My rest," although the works were finished from the foundation of the world. Notice that verses 2-3 makes a
distinction between
US who have BELIEVED and
do enter that rest and
THEM who heard the word but did not mix faith with what THEY heard and will not enter that rest because of UNBELIEF. 
