I haven't used a shangri-la, but I did have a megamid I used for the snow. If you are going to did a pit, at least stake out the shelter first, then dig away. The trouble is how to support the shelter once you dig a pit. I've tied it to a cord between two trees and also lashed trekking poles and snow shovels together to make it long enough (depends on how much you dig).
I see no need for a snow skirt if you are planning on digging down, you need someplace to put all that snow after all. I would be very concerned about using mesh and it tearing when you try to take your shelter down.