I want this game so badly...and I've only known what it was about for like a day. It brought the forums back to life, so I am happy.
Also, I can imagine some possible endings:
Issac actually is corrupt and evil, devil's spawn and all that, this gives Issac a debuff, and the final boss (presumably his mother) some kind of Holy buff. The ability to heal herself, maybe? Anyway, after you beat the final boss, thus committing patricide, Issac goes on a rampage, you are left with an image of fire and destruction, knowing you caused it...
or maybe that's too dark...
It wasn't the voice of god, it was the voice of the devil, and this dungeon has led you to Hell, where you must fight a demon version of Issac's mom, who is shooting fire and things like that. You defeat her and escape from Hell, but now you don't really have a parent...
or (best ending)
You meet your mother without collecting any items, and she realizes that you aren't corrupt after all, you came all this way, through a dungeon of doom, without doing anything corrupting. (Who cares if you killed a bunch of monsters?) She decides to defy God, and let you live. God sends down some giant holy hands or something to kill you, but you hop on your mother's back, getting the ultimate buff as you control the mother now. You defeat the Holy Hands, and live happily together.
So yes, in my mind, each ending would have a different final boss to go with it. Obviously it probably won't happen, given that the endings are already done... or maybe the game got leaked and I know what I'm talking about!

Although, there are also probably five versions of the final boss, since Edmund said there were ten endings. Two endings per boss (one if you win, one if you die) means you get five final bosses.
It feels good to have these forums resurrected. Also, does anyone else
love the music for this game? I'm listening to Thine Wrath right now. It reminds me of the music from the first Narnia movie. I wonder if that's deliberate.
I haven't rambled this long on the forums in forever. Good to see this game is coming out soon. Later!