So what does define pokemon, since my definition is apparently wrong?
Realistically speaking, this is a "per person" answer that you shouldn't be asking others.
I can tell you that *for me* Pokemon main defining aspect is the varied design, and i'll be met with a horde of people complaining about how most recent designs are all boring and useless.
I can tell you that Pokemon defining aspect is that it's the only monster collector RPG with a serious and complicated PvP scene and I'll be met with a horde of smogoners telling me that GameFreaks is incompetent and have no clue of what they're doing.
I can tell you that Pokemon have a enticing gameplay and nice customizability, and I'll be met with a horde of redditors complaining that the games are so easy there's no fun in playing them
You have to find your own answer to this question.
it’ll be interesting to see what happens with Terapagos and Ogrepon next gen.
If you think of it, it's not difficult to predict.
Ogerpon has a terastal gimmick sure, but his form change is not linked to Terastalization and the various masks can carry over just fine as they basically work same as Arceus forms.
Terapagos is probably the same, it'll just lose whatever terastal gimmick it has.
And yet, two generations so far, Mega Evolution haven’t returned. You may call that one too early to conclude, but I doubt that Mega Evolution will return in Gen 10 considering that Dynamax (+ Gigantamax) and Terastalization overlaps with Mega Evolution in terms of power boost that comes with cosmetic change, GF would end up going for another excuse to not use Mega Evolution in favor of another super mechanic that interact with another important aspect of the gameplay, such as Abilities.
And considering how awful the power creep have gone into in SV competitive - part of the blame is nerfing too many old Pokémon to the ground despite not even being problematic in the past unlike Zacian - bringing Mega Evolution the next generation would only make thigns even worse unless GF rebalances the mechanic to some extent.
I would not expect any of the mechanics to ever return unless either
- generational remake happens (which is pretty close, assuming we're about to be getting gen 5, the next in line is the Mega generation)
- they simply decide "ok we don't need to make a new mechanic for this generation, let's bring back a old one".
Fwiw it's pretty obvious to me that right now they're experimenting with "how far" the supermechanic can go. The power budget allocated to the supermechanic had a steady increase from "superform with item cost" to "massive nuke with item cost" to "temporary superform with no downside" to now "permanent superform with up and downside". We can't be in their head for when they decide that "it's enough let's try revisiting a old one now", but they themselves specifically said that "they may bring them back when they feel like it" as it's their way of designing the games (remove and bring back aspects based on what they feel is appropriate. Es, they removed Gyms in gen 7, then brought them back in gen 8)