I'd probably second going with the Fuji X system due to continuity and familiarity of the system.
But it doesn't hurt to see what the competition offers and there're a lot of 'action' in the mirrorless system space.

Sony FF will be out of your budget and probably their latest APS-C models but their older APS-C system are still available for purchase for cheap. I'd personally wouldn't consider Sony for their APS-C system alone as it feels to me their priorities are in the high end FF market. But if you have the money, some of the best tech are available in Sony FF.

M43 is a pretty well rounded system with a lot of lens options. I especially like some of their cheap fast primes like the 45/1.8 (90mm equiv FOV due to the 2X crop factor) and in the case of Olympus, their IBIS and dual IS technology. It's at a stage where hand held long exposures may be possible and I'm talking exposures well into the seconds.
If you're into video, then have a look at the Panasonic offerings.

I like Canon's new offerings for their EOS-M system. But it's a work in progress and the system is still in its infancy. But if their current offerings already fits your needs, then why not.

Nikon's system's not born yet but expect some action as early as later this year (I'm not counting the Nikon 1 system which seemed to have stalled). What it is is anybody's guess atm.