I'm thinking they're going to be a little more broad with "transformations." They've represented that a lot of different ways over the years--flip cards, morph, things that change when they hit threshold or delirium, level up, meld, [[Figure of Destiny]], PLC color-shifted and alternate-reality cards ([[Crovax the Cursed and Crovax, Ascendent Hero]], for example), planeswalkers who evolve across cards, etc.

However, it's hard to think of a lot of really iconic cards anywhere in all those lists. Figure of Destiny was pretty good in Standard in its day, but not particularly memorable. Erayo is probably the most memorable of the flip cards, and that's probably has as much to do with being banned in Commander (and maybe 2HG if that's still a thing) as it does with actually being played.

I dunno. Maybe they'll interpret "transform" in all kinds of other ways. But even going for every form of transformation I can think of, it's hard to come up with a lot to get real excited about for a FTV.