No one is buying Rasp Pi's in the collective scheme of things to run an Amiga OS variant. None.
You could have every AmigaOS variant ported to Rasp Pi and the total number of people buying the things to run said OS variants would be in the fraction of a percent.
So far, 500,000 Rasp Pi 2's have been sold. There's a pretty fair variety of offshoot OS's to choose from, yet I'll still wager 99.99% of them (Pi's as a whole) are running nothing but what the things run natively as a mainstream OS - Linux.
A $35 "Amiga" won't re-invent the glory days. The number of people even running AROS for Pi on a regular basis would be minimal, and if people haven't already crossed the proverbial divide and coughed out $35 on hardware to run AROS on the Pi, what difference would AOS or MOS make.
Even the new Pi is a pretty horrible experience if you want to run a daily driver, GUI based OS on it - even Linux. I find the AROS offerings for it nothing more than a "can we do this" case.
This.
The Pi is a fantastic toy, and it has a ton of useful applications (I use mine for video surveillance), but as a desktop system it's absolutely horrific. Framebuffer drivers were cool back in '98, but trying to run a full-HD desktop with it is just painful.
That being said, it could definitely become a decent machine for AROS if someone wrote proper drivers for it. Unfortunately, it's nothing more than a novelty until then.
