Someone mentioned that Flatrock is currently in a shut down to do some upgrades to the line. That could also be causing a backlog if your car was about to hit the line. I am in the same boat, I waited until now to order so it would not arrive during the winter. I'm banking on sometime in April...
I went with Magnetic for the car I just ordered. I thought the blue stitching would would really good with that. I don't think i will be disappointed in how it turns out.
I'm in the same boat, want to get a mustang and was thinking MY17, but going to hold out till the MY18 full reveal. From what i've seen so far, it's slightly enticing, but any of the potential new options seem to put the car above any price range i would be looking at.