Well, if anything, this throws a spanner in the works. Music Theory hasn't been an open-and-shut case, but it
does say something that every non-echo newcomer so far has been accompanied by new music from their series (They even delayed the AC music to line up with Isabelle!). If anything, this may
decrease the odds of there being a new 'mon in the base roster, but not destroy them outright.
Now we need something to put box theory in peril for fun.
I mean, if anything, the fact that other significant rumors are going around suggesting up to
three unique newcomers brings it into question. The odds of only one being on the base roster, the other two being DLC,
and there not being any more newcomers that haven't been mentioned are...well, not that great from where we're standing.
There’ll be Pokemon fans who will be disappointed that one won’t be added, including but not limited to Incineroar, Decidueye, and Lycanroc supporters.
Well, can't speak for everyone, but I'm not too worried about the prospect. There'd be a year or so of DLC before Gen 8 was out, and they wouldn't jump the gun and add a Gen 8 newcomer early (Only time an early bird newcomer has happened was because Roy's game got delayed!).
And if they chose someone from Gen 7 as of right now...well, there's one who stands out furthest from the rest.