My concern is that scrolling is such a frequently-used action, on my MacBook I'd really like it to be bound to my up/down arrows. That way I only have to hit one button to activate it, rather than two. I scroll messages all the time, much more frequently than I edit messages. (Especially since there isn't a compact theme yet.)
Would it make sense to add an option, "Use up/down arrow keys for message scrolling (note: this disables up-arrow for editing last message)"? That would be very useful for many people while the general shortcut customization feature is being developed.