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I have no doubt a lot of Arceus' mechanics will be in the next game, but I predict they'll re-work the stat levels so each level is essentially 25 EV's and it'll be capped at 500, and getting the levels will be fighting certain pokemon like before as well as using the grit shit.
They'll probably ditch the extra 4 EV's and just have you able to cap it at 2 stats at L10, or distribute lower levels to more. (Like you could have 2,4,8,4,2 from attack to Speed if you wanted or some combination that adds to 20)
If I recall correctly IV's are still in Arceus, just unused, however Alpha's still give the 2+ perfect IV's and would apply to the stats if transferred to a game that uses them.