As Destiny shows, they aren't locked to only following the line art with the Metal Build line.
They can easily give Unicorn and Banshee a unique look that sets them aside from the FF, and frankly given my hatred of OO It would be nice to have something else besides more jerking off of Setsuna.
Between the Metal Builds and Extreme Vs I'm so sick of the bastard that I nearly hate him as much as Shinn.
Well, you have to keep a few things in mind. First off, the Banshee FF Metal Composite came out only a month ago. Second, Katoki's lineart almost never gets messed around with (I say almost because maybe there's an instance I don't know about, but I've never seen his lineart get revised by another artist for a model/figure - I mean, the guy has toy lines named after him!). Third, Okawara's lineart almost always DOES get changed around for plastic models, figures, toys, etc. Look at the Seed Master Grades.
All that said, I highly doubt there will be FF Metal Builds of either of the two Unicorn Gundams. Personally, I am not a fan of Seed an consider the Seed Metal Builds to be a waste of time, so I just avoid those and keep my fingers crossed. Despite your hatred of Setsuna, just think - if the Quanta comes out, there's no more Setsuna mecha left to release, which means they'll have to move on to something else.
I assume they'll do the Strike Freedom at some point, but after that, I bet they'll move on to another series. I'd like a Turn A Metal Build, thought that'll probably never happen. Maybe it'll be Wing Gundam or one of its variations.