The game will be out of beta when it'll be literally completed, means all the regions, pokemons and every possible features be implemented and for that i don't think it'll take any less than 3-4 years i.e. if Pokemon Franchise stop making further regions and new Pokemon.
So, you want to lessen the elite 4 time for so long time. I don't think it'll happen.
But i love your 2nd idea of showing how much time is left to rebattle it.