I believe 11:17 is referring to the unbelieving Jews as "broken off" and the Gentiles represent the "wild olive tree."
First thank you for this thread, it is already good.
Second, I DO NOT KNOW! I am trying to learn. There are statements in the Bible that seem to be often taught wrong.I
Third, I am not dispensational in my thought, The Bible is one continuous story. I try to look at what the Bible says not teachings of the Church or men.
The first half of Isaiah discusses failure and rebellion judgement and destruction of Nations, and He speaks of a REMNANT and a GREAT ROOT that all will be grafted into.
Isa_1:9 Unless the LORD of hosts had left unto us a very small remnant, we should have been as Sodom, and we should have been like unto Gomorrah.
Isa_10:20 And it shall come to pass in that day, that the remnant of Israel, and such as are escaped of the house of Jacob, shall no more again lean upon him that struck them; but shall lean upon the LORD, the Holy One of Israel, in truth.
Isa_10:21 The remnant shall return, even the remnant of Jacob, unto the mighty God.
Isa_10:22 For though your people Israel be as the sand of the sea, yet a remnant of them shall return: the destruction decreed shall overflow with righteousness.
Isa_6:13 But yet in it shall be a tenth, and it shall return, and shall be laid waste: as a terebinth tree, and as an oak, whose stump remains, when they are cut down:
so the holy seed shall be its stump.
Rom 11:16 For if the firstfruit are holy, the lump is also holy: and if the root is holy, so are the branches.
Rom 11:17 And if some of the branches were broken off, and you, being a wild olive tree, were grafted in among them, and with them partake of the root and fatness of the olive tree;
Rom 11:18 Boast not against the branches. But if you boast, you bear not the root, but the root you.
Rom 11:19 You will say then, The branches were broken off, that I might be grafted in.
It seems to me this remnant refers to the ones true to Gods commands and returned to their land.
Paul is referring to the "Stump" that remained saying all are "Grafted into the Tree Root the Holy SEED JESUS.
So I see the nation that rejected God and worshiped Idols went into captivity and never returned AND then the REMNANT That returned were true to what God said and replaced the Nation as God's people. Remnant, Spiritual Israel, God's People, what you call them is not so important. We Christians are Grafted into that group.
YES, God is not finished with Israel The Nation Both the Tribulation and the Millennium will include them. we are told a third of them will enter the Millennium as living people on earth, What God has in mind I have no Idea.
Remember I am not telling you WHAT IS, I am asking what does it SAY!!