I can certainly see scenarios where it's ND, UNC, UVA, and one of Duke/Stanford/Miami going to the B10. Maybe even Kansas or Arizona in the mix. If FSU can't get in right now, I don't necessarily love their chances when there's a myriad of options and people scrambling to get in alongside ND. There may not even be 4 B1G spots available, they might stop at 20 in which case ND and UNC are basically locks.
Maybe the SEC fires back if the B1G expands and grabs FSU/Clemson? But once again, if they aren't valuable enough to add right now, I'm not sure what changes just because the B10 expands. I also don't think the SEC tends to be very reactive.
Who knows, but if FSU ever actually sets foot in the conference, I would say there is a non-zero chance they're a B12 team for the long haul.