I know that Amiga had a RAMdisk in the A500 days but I remember that when I started using mac the second time (about 1995 and OS 7.5 I think) they had a RAM disk. That was on a Performa 6200.
Thye first time I used Mac's was when they replaced the trs80 IN 1979.
The AmigaOS will not be mainstream until it leaves its specific low-volume hardware-dependent routes behind. IE It can run on a G3 so why not have the OS run on old Mac's. Lots of people will try it out on an old machine. Or have it ported to intel so it can be used on an up to date box-shifter cheapo machine.
Come to think of it; paralells with RISC OS there.