Way back when I got my first Amiga and decided to start programming it and stop programming my peecee, I fully intended to learn 68k ASM, as I was well versed in x86 ASM (of which I've forgotten already!), and 65xx ASM (self-taught by TRIAL AND ERROR). But, even back then when '060 boards weren't quite available, there was this talk of getting away from 68k and moving Amiga to some alternate CPU.
I recommend sticking to C (as much as I despise that language) for the sake of compatibility and portability. If tomorrow someone develops some CPU that obsoletes all CPUs on the market and we start running AmigaOS 6.0 on it, there will still be a C compiler for that.