Yeah... If you're looking for new stuff that is a "true mech simulator", you're kinda shit out of luck...
You have Hawken, but as someone else put it, that's more of a mech-flavored FPS. Not that it's bad, but having lived through the "mech generation" with games like the original Mechwarrior games and Armored Core, it's not the same.
You have Mechwarrior online, but last I heard that was a bloody mess.
And you have Titanfall. While I love the game to death, it's also not exactly a "mech simulator", much like Hawken, and more of an FPS with lots of awesome things including mechs. Again, fantastic game, but not necessarily what you might be looking for.
I haven't tried it, but I heard good things about Strike Suit Zero. Haven't played it though. Also I think that's strictly singleplayer?
So yeah, the genre just kinda died, or is at least laying comatose, at least in the sense of Mechwarrior/Armored Core kinda mech game... Maybe with the success of Titanfall (and Hawken to a lesser extent?) other companies might see an opportunity to invest in more mech games. Maybe we'll see a return of the genre.