We have the same dream!
Regarding sponsorship, I am working on a POC with spot instances. If spot instances work there are two items of note:
1) Sponsorship will be more difficult since they'll be created on demand. I think we'd have to managed multiple EC2 Api keys.
2) It looks like it will be very, very cheap.
Regarding "OPEN" - I agree. If the instances are created on-demand, the only item I think we'll need to figure out is how to store the EC2 API key. I am not too versed on EC2 API keys but I am hoping we can create a key for this specific application.