Custom command aliasing is an interesting idea - I think we need to add support for aliasing so we can have multiple names for some of the commands. It would make sense to let people set their own aliases too.
For channel switching - would you prefer a slash command for this, or a keyboard shortcut that opens a channel picker dialog where you can start typing in the channel name and it can autocomplete? Maybe it would make sense to have both.
Would you be interested in working on a /window command?