I only use 220gr subs when testing. I have both mini and micro length gas systems and both run fine with a can. The gas ports were drilled out tons trying to get them to cycle without a can, the hole doesn't need to be that large for running supers normally and subs with a can. I know Alex was working on a smaller block that would go up under the rails but I can tell you that having been shooting 300BLK for 3 years I don't ever shoot my AAC without a can when shooting subs (and it will cycle them just fine).
I don't think most guys will want to buy a new upper/rail to shoot 300BLK on their L. With the SIG Brace I can see more guys running micro uppers but guys want to be able to purchase a barrel and convert.