My main point was that Groudon's item cannot be stolen, Knock Offed, or otherwise manipulated to force Primal Groudon to reverse its Primal Reversion, so it's weird to treat Primal Groudon as not being a distinct option -it would be like saying all of Rotom's Forms are treated as Ghost/Electric, even though it's impossible to force them to change Forms.It's not completely identical. Arceus is whatever type it is outside of battle based on what item its holding, while Groudon transforms in battle if it holds the Red Orb (at least I'm fairly sure that's how it works).
But it's sort of irrelevant what my point was since, yay, Primal Groudon is a real
The Megas thing is interesting for the few type combinations that are impossible to combine except via a Mega -such as Mega Altaria allowing Fairy/Dragon teams. I don't think it affects any current "standard" God choices, but that's OK.Primal Groudon and all Megas now use their altered typing when determining which types you can use on your team, provided you put their altered form in your teambuilder data.
Stall actually does care about losing access to priority, particularly stuff like Poison Heal Gliscor potentially having to deal with Fake Out hitting it when it's trying to Protect. It's not nearly as crucial to stall as to other playstyles, and in particular the -1 priority is most punishing to Hyper Offense styles, but it's not actually irrelevant.Punishment
One alternative that is relatively neutral on playstyle (Overall it probably hates on Stall most and Hyper Offense least, but one could combine it with the existing punishment to "balance" things out) is to apply some degree of Pressure-style effect on every move used -lose 4 PP per move, say, and suddenly Fire Blast only has two uses, Softboiled only has 4 uses, etc.
Holy crapcoded+hosted
Maaaaan I wish I had the time today/tomorrow. Well, I guess I can design a team and try it out come Tuesday...