If they come up with an APS-C mirrorless body with a few good lenses to boot then life might get interesting.
I suppose Samsung and Sony would be the only real direct competitors using the APS-C base.
Samsung's NX series may offer resistance if they stick with the lens road map and if the NX20 turns out to be a cracking body like its predecessor.
Sony I suppose would get clobbered almost immediately given that they have no real lens options still. :-/