The problem is that such technology isn't monetizable. I mean, you can sell the API or library or whatever that you use to interface with the inbox to people looking to develop such software, but the kind of money it would generate isn't really worth the hassle, IMHO.
Amen. Building features isn't monetizable. I wish all these companies would look at what happened to companies like LimitOne. If Google can throw a couple of developers at it and build it on their own, even if they decided to buy you out to save time you wouldn't make that much from the sale.
xobni seems to have plans for something akin to this:
"Notably, Xobni is also working with third party developers to let them build applications with Xobni. By allowing third party integration for its APIs, Xobni becomes a trojan horse for those third parties to access Outlook integration through a plugin. Microsoft Outlook doesn’t offer a friendly set of APIs for people to plug into Outlook, and so Xobni hopes to become the place developers come to for such access"
Doesn't seem like a large stretch of the imagination to think they will do this for webmail as well, especially with the "leak" of their Yahoo mail integration.