Scroll back is the only feature missing that would block me, assuming you permit changing the colour mappings.

I generally run five or six desktop terminals, only one of which is running screen locally. I more normally run something like screen to get persistence across suspends on an SSH connection. I usually don't do much side by side stuff in terminal so tmux isn't a big win for me. Also tmux didn't run on cygwin for the longest time, and I expect the same experience on all my platforms.

However the big tmux users in my life would still use it as is.