If randoms & arranged team would have split matchmaking, the arranged teams would wait 30-60 minutes to find a match. Randoms would also wait longer, it would just be a bad change overall.
However I think randoms should not lose any ELO/rank if they lose vs arranged teams.
thats about as wishful as having less elo loss for performing better then everyone on your team and being dragged down into the Elo mealstrom hell that is coh2