As a fan of the thiccness, I think the strength of Sylphy is the variety in the gameplay of 2, expanding on the fun "theme park" of minigames, little fun encounters, and different "worlds" would probably work really well for a Sylphy's slutty variety hour type thing. Like... the Mario 64 castle, except instead of jumping into paintings to earn stars, it's a wide variety of lewd situations for the chubby heroine. Definitely subject to scope creep, but something like that sounds fun.
But now that you mention platformer, a metroidvania with her in the lead role also sounds great lol.