Scrolling through messages in the current channel is at least awkward, or not even possible, with keyboards that lack PgUp/PgDn/Home/End keys. For example, the MacBook Pro and Apple's Magic Keyboard do not have such keys, but they do offer arrow keys.
Therefore, it would be great if Mattermost keyboard shortcuts could be customized by users. The main customization I would prefer would be to use [up arrow] and [down arrow] to scroll through messages. (I have no need for editing my last message, so I wouldn't care if that shortcut became unbound, or I could rebind it to something else.)
I think all the keyboard actions should be made user-customizable in Mattermost.