I think I can field your questions haha. At least the first one.
Back in the days of ORAS, there were a few other Pokemon that were slated for getting a Mega Evolution, but eventually got skipped over due to the lack of a finalized design before deadlines. Now that we're leaving the 7th Generation, will more Mega Evolutions slowly be added to the existing roster as it has with all other even-numbered Generations?
Pokemon tends to alternate a bit between focusing on "additions" to previously-discovered Pokemon and focusing on brand-new Pokemon. The big "new stuff" gens were mostly the odd ones, as you pointed out -- Gens 1, 3, 5, 7. The ones that did more augmenting of the past were mostly Gens 2, 4, and arguably, 6, although I think 6 straddled the line a tiny bit more than Gen 2 or 4 did (although I'm sure many will disagree, and I can understand that too).
Whether Gen 8 will follow the trend of the even numbered Gens remains to be seen. Sadly, though, I wouldn't hold my breath for new Mega Evolutions
. It really does seem to be something unique and special to Kalos; but you're right -- with the big influence that Mega Evos have had on VGC and competitive metas in general the past while, to some people it would be nice to have some new ones to add to the roster rather than the creation of yet another mechanic (ex: "Armoured" Pokemon that can attain mega-esque stats) on top of Z-Crystals and Megas for players to think about. Fortunately or unfortunately, depending on how you see it, we're more likely to get a new Pokemon-boosting feature (ex: Armour) than new Z-Crystals or Megas. But hey, anything could happen!
On a similar note, with the introduction of the 2019 VGC series, the format went through a substantial shift with the introduction of the Sun, Moon, and Ultra series, which placed restrictions on both Mega Evolution and Z-Moves. Is it safe to say that future VGC seasons will follow a similar format from now on?
Now, just for anyone reading this wondering about VGC metas (not necc. this poster): typically, when new games release, the first format is limited to the regional Pokedex of that region, and the limitations of that region (ex: for VGC 2020 it's likely going to be SwSh regional dex, no megas, no Z-crystals). After that it's typically the wider Pokedex, banning Mythicals (the usual suspects). After that we go into a format that allows 2 Mythicals and no other restrictions (aka "GS Cup"). If anyone's wondering, my fave is the first
Ofc we don't know the answer to your question, and it could really go both ways. With 2020 likely being SwSh-only, like I speculated, I don't think Megas and Z-Crystals will even be legal. That being said, the Sun/Moon/Ultra series did really shake things up and keep people on their toes, forcing top players (the ones with the money to travel or living in event-dense areas...) to come up with 3 teams in the season. That's an element I feel like they'd be keen to maintain. Imo it would be fun either way, and like you, I'm curious to see how they handle it!
Edit: I know nobody asked, but PLEASE GAMEFREAK, I know you said it wouldn't return because
kids these days don't have the patience to grind through it and appreciate it, but please
bring back the Battle Frontier ;__;
Also, direct predictions: early game Pokemon, Steel-type Eevee evo, new mascot like Lucario or Zoroark, or Legendaries. Leggoooo
