The M50x's have coexisted along with the regular M50's for years. I've read a review or two that claim recent versions sound different but haven't heard them myself. I don't really want a detachable cable (or the price increase) so I guess I'll keep using my current pair until they fall completely apart.
I'm not sure what "the bass is hyped" means.
I think the M50's have a pretty flat curve overall and I've (anecdotally) seen countless engineers and musicians who swear by them. They are pretty popular in home studio setups and professional recording studios.