Out of curiosity, why do you love iTerm? It's always struck me as kind of ugly (especially its preferences). And AFAIK, the only real feature it has that Terminal.app doesn't (besides the native tmux integration, because I still don't really see the point) is support for apps customizing the 256-color palette on the fly (e.g. the initc capability), and wile I really would like to see Terminal.app gain support for that seeing as how the xterm-256color terminfo it uses declares that it works, lack of support for that isn't a good enough reason to switch away.
The coolest feature of recent versions of iTerm is the "Selection respects soft boundaries" feature: with it on, iTerm will detect vim/tmux splits and constrain the selection to just one side of that split. For my workflow, at least, it makes a huge difference.
Also, if you start tmux as "tmux -CC" iTerm will open the tmux session in a new window, with GUI tabs for tmux tabs and GUI splits for tmux splits.
iTerm has https://github.com/ravenac95/sudolikeaboss. Integration of your 1Password passwords with your terminal, which makes life amazing. Typing and copy/pasting passwords(not to mention copy/paste is not exactly secure) is a major time-suck. I'd love generic support for this feature in something like Alacritty.
Interesting, but I don't think I've ever felt the pain of not having that. It's pretty damn easy for me to use the global 1Password hotkey to bring up 1Password Mini, type a few characters to identify the login I want, hit → to expand the login, ↓ to select the password, and ↩ to then copy that password, which I can now paste into the terminal. It's not that hard.
Unless you're entering your sudo password with every other command you type, it doesn't seem like it would make much difference either way, it's pretty darn fast already.
So I guess we all need a faster term emulator :)