2: Time and money required to port applications.Without app's, an OS is worthless.
Most current OS4 have already been ported to x86, and even better: AROS. So no time nor money involved here...
3: Oh hey there AROS! What functionality does os4 give that AROS doesn't ?
It's the same with Linux PowerPC, MacOS PowerPC,... What functionnality does OS4 give than these don't ?
4: Most overlooked:
Hardware support.
AROS has been around for years and still supports a fairly limited range of hardware.
Well, it's fairly limited but still a lot less limited than current OS.
But going x86 isn't supposed to bring so much hardware choice. It's about to give access to cheap hardware. You could select for example a motherboard from ASUS, and only support this one.
The assumption in these threads tends to be "we could run amiga OS on any PC and it'd be rad". And that would rad, but it won't be reality.
Of course not.
5: User base.
Is there any actual user base in a world saturated with mature OS choices ?
Well, is there any actual user base when you produce 500 machines per year (and I'm optimistic)... I don't know what would happen if it was available on x86. What's sure is that hundreds of millions of machines are sold each year. That's certainly a lot more potential than anything produced in the Amiga "market"... 0.001% of this market would mean 2000 new Amiga users a year...
Pessimistic ? Maybe
Optimistic ? Maybe

But we'll never know unless they decide to make the move... And as we would say in french... "qui ne tente rien n'arrive à rien" (Nothing ventured, nothing gained)
What's sure is that PowerPC is dead-end, unless you target some embbed market, which clearly isn't what Amiga users do.