This is a challenge i've seen a few streamers attempt, one notable example being Fergus, in which he would start a new steam account and try to rank up a char in the online all the way to TGP, initially during a 12h session, and later as fast as he could. I dont know whats the site position on speedrunning online challenges, but considering this is basically the main competitive mode of the game i think it should at least be debated if it could become a speedrun category.