“…developers have asked us a lot for a market place where we’ll help them sell their extensions to our users including a revenue share so we’ll also make some money from it. “I’ll be very surprised if we don’t go down that route.” - Google Wave to have application store | News | TechRadar UK

This will be a very important development in the success of Wave. The iPhone has grown enormously by making high quality apps simple to pay for and receive. The key difference for Wave will be that the protocol is open for anyone to extend, and the main client (the Google Wave interface) is web based.

I predict this will mean a lot more extensions will be made open source or free. Of course it’s highly dependent on the quality and user experience of the store. If a developer can make an extension open source, but still make it available in the same marketplace many will choose to do so.

Keep in mind too, that over time other clients will emerge that will access the Wave protocol, and it will be interesting to see if the marketplace will extend to such clients.