Looks like you can set a password on it now, which is cool (though I personally like having linux perms govern access to my screen/tmux). Multiinput sounds interesting as well, though in the past that was a feature I thought I'd love to have, but once I had I never use.
I'm glad to see Screen is still getting some love :-)
I ran screen for years before finally switching to tmux around 2011, and it's impact is still heavy as my tmux config is still rocking my "make tmux controls like screen while transitioning" setup which I intended to be temporary. Ctrl+a from my cold dead fingers