I'm really not sure about that, to be honest. Morgoth is an extremely powerful entity, even as far as gods go. And you really want to fight someone you can't kill? Morgoth's immortal, in case you forgot, and I'd rather avoid scenarios where Kalama will have to step out of his designated role for the RP, which is to guide us. If you guys really want to do that, though, I'll do it.
If you want a more powerful end boss than Ancalagon, I'll gladly pull Sauron into this with his full power, meaning he'll be more than a nameless lieutenant this time around. And since he has yet to pour all his lifeforce into the One Ring, we'd have to actually mortally wound him to defeat him instead of simply separate him from the Ring. Even if this means the Third Age will basically never happen, I feel it's better than pissing off Morgoth. But, really, who's gonna miss the Third Age? There wasn't as much awesome stuff happening then, after all.
EDIT: Anyway, I'm mainly waiting on a reply from Rawk before posting so I can get all responses up at once.