Cash or no cash, I believe the key for a developer is working on an interesting problem + having impact. If you have real companies offering real money for a product that don't even exist, at least the developer can be convinced that his/her work will have impact.
But I think a strong trend will be that less experienced and less skilled (and over-confident) developers will be more easily lured. How do you counter this trend when recruiting, and filter for the one that is skilled enough but still can be lured? You can't just take any developer to be solo developer for a startup (much harder than team development), especially to work on somebody else's idea.
