Quick note: "Please stay in touch" as industry speak is actually a good thing to hear. It means - I have nothing concrete now but please keep checking in with me as there is something about you or your project that I like. It is an invitation to keep in touch in case something happens or changes with you or them, and more importantly the person believes it could. This is along the lines of "Please remind me about this...." or "Check in with me later...." Frankly, these are the best things you'll hear beyond a yes. Believe me, if people don't want you to contact them or really don't like your or your project, you won't hear anything. And that's the norm. But if you hear this, you really must actually stay in touch. Mark your calendar and then do so. Such invitations aren't all that common, and you should respond with grace and thanks. I've done so for over a year, reminding someone about a project as per his or her request. And it paid off.