this sounds a lot like diablo2's cow level. i guess it doesn't hurt to have that battlefield at the end of the game but it can never hurt the game even if it's early or middle of the game progression.
i'm still wondering about the scope & breadth of the battlefield; how big/small can it be? just how far does randomness factor goes in it? does it affect only items & enemies & NPCs or does it affect even the environment itself? how does scripting work if extreme randomness is at play? or maybe there isn't any?
i guess the ones with NPCs & certain quests may have more scripts than ones that have only hack & slash factor.
mybe battlefields can be a rarity in such a way that players need to be observant enough to actually find rifts or maybe clues to rifts that have very good rewards should they find & complete the quests related to the rifts. almost an easter egg, except it's very relevant to the game environment.