Could not be happier to see this coming.
This may seem niche, but I specifically hope they fix this very particular bug where older cardstyles get applied with newer set symbols. You can see what I'm talking about here. I owned the Guilds of Ravnica Healer's Hawk cardstyle long before Foundations came out. But I am unable to use it without the FDN logo overwriting the GRN logo. (also the picker behaviour is mildly broken in general, as you can see).
In some cases, like this special ZNR treatment, I can't even use my cardstyle at all: https://imgur.com/exIF77H