Custom user content is a logistical nightmare if it's not built as part of the network architecture (which it isn't in 3DGS).

You could enact a solution that uploaded the custom logo to a web server and then asked each player to download it when needed in the game but I think it would be a nightmare to script out, manage, and implement properly.

Furthermore everytime the logo changed or a new player came on board you would have to re-upload and re-download and that could eat up your bandwidth right quick if you don't manage it properly.

My opinion: Can be done but I daresay it would be the only thing one person would be working on for a long time to get it done.