The ability to spectate other players while they play "Not Submitted" maps would be a pretty neat idea. I've made thought out a "Small" Concept which might get it to work out somehow. Would require quite a lot of work to implement it though.
To start everything off, when a player starts to spectate someone who isn't playing a ranked/submitted map they just get a message that they don't have the beatmap. Instead they may now get a new window which says something like "Request map from player" or something like that. Where the one who plays it gets a request before/after the map is complete to export and save the map on the server for couple seconds until the map has been retrieved from the spectator. This would all happen automatically so players don't had to worry about using alot of time just to get the map to the other players. That way the "Not Submitted" maps could be brought back into the game (Kinda). And you didn't have to wait for the player to finish the map before you can start to watch him play again.
It might sound unclear to begin with, but I'll try my best to explain any questions you might have around this topic.
To start everything off, when a player starts to spectate someone who isn't playing a ranked/submitted map they just get a message that they don't have the beatmap. Instead they may now get a new window which says something like "Request map from player" or something like that. Where the one who plays it gets a request before/after the map is complete to export and save the map on the server for couple seconds until the map has been retrieved from the spectator. This would all happen automatically so players don't had to worry about using alot of time just to get the map to the other players. That way the "Not Submitted" maps could be brought back into the game (Kinda). And you didn't have to wait for the player to finish the map before you can start to watch him play again.
It might sound unclear to begin with, but I'll try my best to explain any questions you might have around this topic.