I just called my local Apple store and was told this exact same thing. When I mentioned that I heard they would not have stock if the iPhone 7 Plus on launch day she just said "Where did you hear that?" She put be on a brief hold to go check on some stock information for me and said that they WILL have stock of all phones tomorrow. It might be limited stock, but they will have some stock. As far as the days after, there's no guarantee they will get more stock in Saturday for the new reservations that will begin, but she said I can check online Saturday morning and see if there are any available.
I'm trying to get the 32 silver 7+.
EDIT: Now to decide if that info is enough for me, or if I should call my other local Apple Store. I live right between two of them...
I would think that most of these stores would have received their shipments sometime today for launch, and if she put you on hold to check what I'm assuming is their physical stock, I'd say some stores will have walk in allotment. I think it would be too much work with too little time to reallocate 100% of the store walk-in allotment to IUP customers, especially if many of the walk-in allotted phones had already been packaged and in the shipping process.