Couldn't one expect at least a job offer?
BTW I worked in a startup once and a guy, who was developing opensource plugin for our product, applied for a job with us. The owner (a known blogger BTW) said "Why hire him if he's already working for us?"
Not only you had a person that already knew much more about your product than the average potential hire, but a person that probably was interested in your product (and maybe knew what users wanted) too.
Because you do not want him to abandon the project if it is useful to you?