@admiralandy if you look at the spacemarine codex then they have already effectively squatted the classic spacemarine.
And given the extra primaris-variant troop types they’ve added you’d be a fool to field any of the ‘old’ troops.

It’s kind of standard GW tactic when it comes to updates for any faction TBH.
stuff gets released, stats get fixed after a few tournaments and then the cycle restarts (there is a funny parody video about this on youtube somewhere).

I kind of doubt they’d do a Heresy 2.0 or anything remotely similar, because that’d threaten their main line 40k.
It’s the same reason why the 40k Apocalyps rule set was a one shot / blink and you missed it kind of deal.
And it’s probably why they turned Killteam into this atrocity with a release schedule that only ever is going to update 2 factions every few months … (they did a compendium and it is clear it only exists to ensure fans don’t stray from the herd before their favourite faction gets the new book & box set)

Anyways …

I think it is safe to say that as far as the 40k lore is concerned that there is plenty of space for a faction like the squats to be re-introduced. Either on a planet that had been hidden by warp storms or as part of a Horus Heresy era update.
I kind of doubt they will do any HH era updates for factions that aren’t spacemarines, because the focus does appear to be spacemarines vs traitors. No HH era Eldar or Orks. At best a few related factions like AdMech or Imperial Guard.
(I know … Squats were kind of sort of mentioned as demi-humans that could be in an Imperial Guard army raised on a high grave world, but squats were also supposed to be an unique culture/race of their own)