Do you think game developers could submit wallpaper designs for AG3 themed with their games? Of course, assuming there will be an assessment over the content.
These type of questions should best be asked in the Armor Games v3 Forum as they clearly have AG3 as a topic.
Basically, nothing will be changed on the current version of ArmorGames, AG2.
As for the statement on developers' backgrounds, there has been a discussion about that, even uploads from the users themselves... but it always comes down to the possibility of misuse with profanity in the end.
Let's hope they will hold those great competitions for backgrounds like Carlie did with the armatars in 2009 and thus expand on the current set of 5 colors to be used.