Depends what is meant by viable. I'm currently building a new classic AGA machine but that doesn't mean I consider it a viable platform, it's just the only one I'm really interested in.
I was getting interested in OS4 after Hyperion won their long running legal last year but since that time its opportunity to become a viable platform has been waning (along with my interest).
Although MorphOS looks very nice, I don't think it will ever become viable as a PPC based OS running on second-hand HW and a move to x86 will be very costly and will therefore probably never happen.
Obviously UAE (eg emulated Classic OS 3.x including FPGA reproductions) will be around for a long time and will probably end up out lasting the next gen boys
The classic market is actually doing 'ok' with enough new interesting HW and software getting released or being updated to take advantage of the new HW.
I think AROS is the only one which really stands a chance to considerably grow its user-base and become a (somewhat) viable computer platform (as in 1% market share at best).
The trouble that all of these Amiga like operating systems face is that the computer world is constantly moving forward and by the time AROS gets to same level of performance/stability/usability as UBUNTU today (which might take another 5 years at this rate), we’ll all be using Cloud based OS’s like
Google Chrome OS
