I would consider Kadabra abandoned at this point. I also consider formes to be abandoned as individually named cards. Most formes get equal-ish representation in art these days though. It does make tracking prints kind of cumbersome since a Pokemon like "Wormadam Plant Cloak" will technically never be printed again, even though she'll get a normal Grass print.
Pokemon like Deoxys are a good example of why I think formes should continue as individual prints. I.E. an Attack forme print and a Defense forme print should hypothetically have different attacks, HP, retreat, etc., and this rang true in the one set that saw Deoxys have named forme prints (Legends Awakened). Having a single Deoxys card represent all four formes these days seems kind of lazy to me. I'm not saying that one set has to have 4 Deoxys cards, but by all means they could spread out the formes across many sets. A "Deoxys Defense Forme GX" or whatever would be cool to see.
Another Pokemon that definitely needs individual forme prints is Castform -- and you probably noticed in its upcoming print it only appears in its normal forme. I think TPC is a bit unsure how to approach Castform now that they've scrapped the mechanic that allowed it to function as it's supposed to, and it might explain why it didn't appear in any ORAS-era sets despite playing a role in the story.
I am unsure about whether the Baby Pokemon are abandoned at this point. They are certainly neglected, but I don't see why they could never come back. It's important to remember that while it's fair to approach the Babies as having contributed little to the game (though Mime Jr. saw a lot of play, iirc), the other side of this hobby is collecting, and there's fans of baby Pokemon (heck, I like Bonsly) so I think they should be printed again in some form or another even if they aren't mechanically interesting.
It's also worth noting that Riolu regularly gets printed despite being a Baby Pokemon. If they went a similar route with the others, where they are standard Basics, I personally would be happy with that. Or make them all optional Basics, e.g. Pichu or Pikachu could both be played as a Basic, but give a little bonus if Pichu is in play as a part of the evolution line.
I am personally not yet ready to say the remaining Megas are abandoned. If there's anything we learned from the XY era, it's that TPC gets hung up on old stuff. If trainers like N and Skyla can be printed in the XY era in lieu of the new characters, despite being many years out of date, I don't see why Megas can't be printed in the future too. (Ideally as promos though; it'd be kind of weird having EX in a set again.)