I got fit for my T100 in September 2019, coming from 718 AP3 I was looking for a smaller profile in the scoring clubs. Absolutely, love them and had accepted they are a world apart and I was going back to traditional lofts and that would bring a difference in yardage. But like you, gutted when I found out about the T100S, as they would have been perfect, I’m going to assume the fitters were unaware of the T100S coming.
Anyway, pulled the trigger at the weekend, and the T100 have been replaced by the T100S in the 7-GW, I went for the 5 & 6 iron in T200, to blend in my U510 4 iron. Feels weird changing clubs after 9 months.

They do - I'm not 100% sure I should be saying this but what a forum if you cant tell the truth....

Titleist arent advertising it but they are letting you swap IF there is a performance benefit. I pre-ordered the T100 and got them on release day but had them bent 1* strong, adding more offset and changing the bounce etc - not ideal. A few months later they announce the T100S - the club I 100% would have bought had they been in the original line up. My pro spoke to Titleist and they agreed that if I went to their fitting centre/fitting event and hit them side by side and there was a performance benefit then I could have the heads swapped, keeping my shafts and grips.

I now have a nice, brand new shiny set of T100S in the bag and love them.