you mean by the time OS is ported to ARM, most AMIGA fans will spend their last days in a nursery home?
Not sure how old you are, but I expect ARM (or more precise cheap ARM like used in rPI) to reach that level of power in a few years.
As to porting/polishing the OS..... *shrug* AROS sure has the resources to do it in <5 years, but those resources are spread thin into 2486 directions, MorphOS hasn't really started, real development on AmigaOS68k is hampered in red tape and don't even get me started on OS4.