Sue!
Honestly, I'd buy anything that blooms really late if I thought the flower was pretty. I've added several dips and a couple of tets just to extend my season.
What I find most frustrating is buying a late or very late bloomer and having it start blooming midseason for me. I bought multiple plants and had this happen to me. I've learned to only buy if confirmed by someone in my zone first (I'm the same zone as you).
So if you can breed some that are reliably very late in your zone I'm sure you'll have plenty of customers!
