If we are getting a Ferrari (especially on this month with Ferrari winning Le Mans) I gonna bet that we will get the 599:
A car that is present on GT HD (which I think it was the car on the box art?), Prologue, 5 and 6 (and the datamined list!). I personally prefer the 599 over any other model!
There are 6 Ferrari cars on previous games that are currently missing on GT7: California, 599, SP1, FXX, F1 2007 and F10.
We probably will never see the F1s again. Between the California/599 and any "modern" Ferrari like the 812 or 488, I'm betting on the 599.