If you want either ARM, or modern hardware/power, AROS is your only option.
If you want affordability, and an inbuilt emulator rather than a 3rd party emulator for system friendly legacy support there's MOS.
If "the name" is important there's OS4.x.
Seems pretty simple really. They're the options. Pick one, or not, up to you.
In regards to whether the ppc systems are underpowered, then currently, yes at times, and it'll only get moreso with time. Already theyre pushing the limits in some areas, and those areas are only getting heavier and heavier in the "modern" computing world. Slowly but surely more things will become out of reach. Already some containers for 1080p codecs (and some codecs themselves) are too heavy for even the most powerful ppc hardware available, and 1080p can only be seen as a medium resolution these days.
The internet is also getting heavier and heavier content (again, some of which is a strain at best for any ppc hardware). 3d rendering speeds are also archaic in comparison to the modern world.
If you want an idea of what the experience might be like, think of how it might be using pc hardware from around 10 years ago (Athlon/early p4 through to early athlon64/late p4 eras), but without full use of that power (less efficient drivers, features lacking, etc.), because really that's what it is.
Enjoyable enough, but within the context of modern computing they will show shortcomings at times.
