Eternamax Eternatus is the first time a Pokemon has form in official games that you can't use. This has been a thing in certain other Mons series for quite a while now, but this is a first for Pokemon.
(This has been done in fangames before.)
That means even if we get Black and White remakes with the original dragon, it's probably going to be not accessible to players for lore reasons or whatever the excuse is.
Why do we even live, ,only to suffer?