'd guess that as long as GCC exists for the platform, it's not out of the realms of possibility. It all depends on how financially viable it would be for BRL to produce.
I wouldn't bet on that. I don't think the bmx compiler just works like a preprocessor, spitting source code for some high level language (say C) that is understood bu GCC.
At the very least the compiler actually spits ASM.
So to retarget the platform, the whole "bmx intermediate code representation" to ASM part must be rewritten. This is not necessarily the hardest part, but it is significant.
And PocketPC certainly don't run under i86 nor PowerPC.