Ah, rats. It looks nice but to save others a bit of searching, if broadcasting to multiple panes is a requirement for you (something I use often in iterm2), it's not yet supported and not planned for support: https://github.com/wez/wezterm/issues/2658
Wez left the issue open and said "I personally have no plans to implement this any time soon.", so I have to imagine he's open to PRs. He just has other things to spend his own time on.
