You have made my point....there is no way any can know “who” Israel will be ‘at that time’ or ‘how many’. The fact is whoever survives the tribulation will indeed be Gods once again...and that very well may mean “all”. I believe completely that it does mean “all” and there will be many.
That’s mere speculation on your part because Romans 11 says nothing about “surviv[ing] the tribulation” as a precondition any other futurist mumbo jumbo.
As the author demonstrates, in context, the only thing Paul can mean is that “all Israel” refers to the elect ones, the remnant, from among all the natural branches that are being and eventually will be grafted back into the root.
What’s odd is the futurists whine about how non-futurists allegedly don’t deal with the text of Romans 11, yet resort to all sorts of odd claims that are not in the text to justify their theories. “Survives the tribulation” Really?