I personally love the server banner but it needs an upgrade, especially on mobile. The quality becomes extremely low on mobile and a lot of the banner becomes faded within the discord background. Lots of users like to put text and branding in their banners and with the quality being so low it's hard to read.
GIF - I can upload a GIF as a banner currently but it does not move. I personally think it would be a cool idea to have a moving server banner upon my channel lists. This feature in my case would benefit my audience with server information. I'm sure there would be plenty of use for this in multiple communities.