So masternodes will still be used for mixing?
This is a disappointment, I must admit

I don't remember this. I'm just working it out with what we're given. Still, I'd think this would be an excellent solution. No need to wait for blocks, how ever many MNs you have, is essentially the number of rounds. Seems logical to me.
Maybe there is another way?
I sure hope it won't be something that obscures the blockchain like Monero. I don't like something I can't check on.