Casual Queue Without MMR?

If they released a specifically "Casual" queue, where your placed roughly according to MMR but the value didn't change, where you could play like trash and try new heroes without worrying about "losing ranks", what downsides are there?

Smurfs pub-stomping seems to be the only one I can see, which can be countered with a win-streak/loss-streak counter, making you queue in "Normal" queues for X-amount (maybe 8-10 games, without leaving) to readjust your MMR for balancing reasons

Maybe this is dumb, but I'm interested in what people think about it