The idea of restricting new players from ranked is a step in the right direction in my opinion. But level 10 is still way too low. I think that you should have re-uped at least once to play, maybe even twice. Anything lower then that should be restricted to social.
I think a similar system should go for Horde. Where to play each increasing difficulty level, you have to have completed the previous difficulty. So to play normal, you have to have completed casual, to play hardcore you have to have completed normal, and so on.
I understand that it is a small player base. But I would rather wait longer periods of time so as to have more balenced matches.