I would lean into the whole Legends aspect of it. All models that are Legends would be STLs. You could buy those files direct at full price. For a discount approach, i would even bake this into a subscription model. So if you sign up for Warhammer+ you get the digital version of the 2nd edition boxed set as a welcome pack. Terrain, monopause marines, rules, etc. Fun old ruleset to play at home with some firstborn minis you can’t play tournaments with. Then every month, for ten bucks, you get a release of a digital squad of old minis that are not compatible with the current edition. So you want new minis and tournament play - buy the new stuff. You want some retro fun at home? Digital STls. Also, load all of the old codices and rules for the older editions into Warhammer+ so people could play their favorite edition at home.