We did mobile passport before heading home and were extremely glad we had done so. Same situation in Miami - very few people in the MP line and hundreds in the main line.

We were also leaving SXM from the lower level which was incredibly cramped and sweaty. We then crammed into a bus to get to the plane. It was not great for a departure experience, but I figure it can only get better before our next trip! ( I am knocking on all the wood as I type this).
When we stopped in the Dominos, it appeared they aren't actually cooking anything there and everything is being driven over and kept in warming bags, hence the sellouts. I think they'd be wise to skip all of the weird sandwiches and pastas and just stock more pizzas but what do I know about running a ghost McDonald's in work-in-progress airport.