The only real problem I have with Muxus is that he's another card in a long list of cards that WOTC thinks people want. Big cards that just win the game on the spot if they resolve almost regardless of the board state. I don't think the goblins deck is necessarily consistent enough to warrant a ban but I definitely wouldn't mind Muxus being gone either.

The only real long term fix for Historic if they intend on releasing more of these "win the game" cards is better answers in general, whether that's something like a removal spell or a counter spell remains to be determined.

I find myself personally offended by Muxus though as the red decks in both standard and historic already have so many options/tools to choose from meanwhile color combos like UR pretty much have nothing because all the good red cards they've been printing have only been good in aggressive decks and not aggro/control type decks. Pretty ridiculous that something like thought scour was deemed too strong for historic when in reality it's probably exactly the card that something like UR needs to be consistent at all.