For 1 - there's actually a nice proposal from WezTerm to make this an all-purpose general protocol that I hope happens: https://github.com/wezterm/wezterm/discussions/4889
For 2 - I think this can be achieved with scroll vertical/horizontal scroll regions (which should also boost performance a bit). I hope to implement this in the future.
Would it make sense for Zellij to also support the tmux control mode protocol, and interoperate with terminal emulators that support it?
Another thing (less ambitious): is it possible to have an option to integrate with native scrolling? Like shpool [3] does. I suppose it's not possible to enable it by default since it has a frame around the session, but maybe this frame could be disabled if I want native scrolling back? Native scrolling helps mainly with navigating by clicking on the native scrollbar that most terminal emulators have (mouse scrolling works on Zellij though, which is very cool).
[0] https://iterm2.com/documentation-tmux-integration.html
[1] https://github.com/tmux/tmux/wiki/Control-Mode
[2] https://unix.stackexchange.com/questions/189805/what-termina...
[3] https://github.com/shell-pool/shpool