simple title, simple premise. everything is still hypothetical.
I already painted stormtroopers. If I can't use those troopers in this new game I'm not going to get it. I don't want to paint a second set of troopers. FFG should understand that once players invest time into painting a mini they do not want to reinvest in painting another nearly identical miniature. GW did this with many edition changes in their games and that kind of treatment is what lead to the market vacuum you are intending to fill. you have an invested customer base, don't throw it out.
It's unknown how compatible IA and Legion figures will be. so far we know a few things for sure.
The bases of models like the AT-ST, trooper transport, Bantha are not compatible.
This storm trooper upgrade card is not promising. this is the sort of list building option that can easily be included on the core unit card. the existence of this card makes me fear that they are explicitly trying to exclude their previous IA miniatures from this game.
I hope this is not the case. I hope FFG will sell a "conversion Kit" allowing IA models to be used in legion that includes bases that large IA figures can slot into and plenty of extra stormtrooper +1 cards.
I hope this because I am the target market and if FFG can't serve that they are not going to have a good time.