Even if this coin was premined, I don't think the developers have bad intentions. They've been giving a lot away, including 10,000 Mintcoin to everyone who liked their Facebook page.

I personally received 50,000 for writing an article on my website involving Mintcoin, that was a nice surprise  

I still agree that the address should be public though. Developers who want a coin to be taken seriously shouldn't be hiding anything at all.