Community day...

We don't know. My guess would be maybe in the far future but nowhere soon.

I’m kinda half expecting some sort of weak Pikachu variant for December’s community day, as part of some sort of lame cross platform promotion for Let’s Go Pikachu, Let’s Go Eevee during the holiday shopping season .... sooo that will kinda be the same Pokémon

Probably eventually because there seems to be demand for it. Hard to say when but probably not in a while, they don't want to hurt attendance of first-time CDs with people thinking "I'll just get it later".

My best guess is that on the one year anniversary of CDs we get a joint CD with all 12 of the CD Pokemon sharing spawns and all the moves available.

I'd give that about a 2% chance of happening.