FZ may well get 787's in the future but I think the reality at the moment is its too big a step up from the 737-800.
As someone has already mentioned the best aircraft fit for FZ currently is a 757 so there is more chance of them ordering 737-900ER's (which they already have options for) and will get delivery dates a lot sooner than any 787.
I'm not clever enough to do the sums but the 737-900ER's are being used to replace 757-200's at Delta so I assume they have the legs