Oooh interesting

Ok so thoughts
First off, the significant investment THREE Feats would be in o5e is ridiculous, so I really hope there's more chances to take them then...5 max for most characters, competing with stat increases. Thankfully even if not LU has other choices after 3rd level, but would love to see a reliable Feats setup that doesn't shirk any sense of balance for "It's an optional rule!" as well as reliably letting you engage with it, especially with rolled stats being around still. Also assuming Vuman is gonzo.
Speaking of gonzo, glad to see Bladesinger in this Psuedo-Prestige system instead of Wizard just being the best Martial.
A couple of these have me REALLY intrigued. "Vigilante" always catches my attention, and I'm hoping "Untamed" might feel like the 4e Warden. Warlord gets all the love but Avenger and Warden are my faves from it.
I also definitely agree with the sentiment that not everything
has to be strict class choices. We obviously don't know the exact benefits, but like, conceptually, I see no reason for Eldritch Archer or Mystic Theurge to be Wizard or Sorcerer specifically. More flexibility, especially as someone who loves Sorcerer and hates Wizard, would be ideal.
Concerns are like. First, "Multiclass Feats" seems unwieldy since there's already "Multiclassing", and Multiclass Feats mean something different in 4e and PF2 and it pulls the mind towards that. Prestige Multiclass, or Fusion Multiclass or something would probably read cleaner. Then, going back to what I mentioned about investment, if Feat Progression is the same as in 5e. Assuming "3 levels in X" is standard entry this seems REALLY potent. 3rd is already where you get like 70% of the Subclass power, and enabling one of these and that at once worries me it might end up a 3.5 situation where Prestige Classes were THE way to build. If you like a certain one of these, especially if the later Feats have higher specific level requirements, it takes up a LOT of build space and might feel like "Playing the Feat Chain" like o5e had "Playing the Subclass". Basically my concerns lie in Subclass and Feat design neither of which we've seen, so these sit somewhere between Concerningly Potent and Incredibly Cool.