You are dead on. Apple did GC bonuses for everything last year. They'll do the same this year, including the iPad Pro. Probably stick with the $50 number.
The question, then, is if third-party retailers will have discounts. At this point I'm guessing not, mostly because they won't have any stock in the first few weeks. If for some reason a B&M third-party has stock, they'll only discount the base model.