Helping one application support many interfaces

These days it's really hard to make one application that supports all the interfaces it has to support from mash ups like Facebook to every kind of mobile device, mobile phones and net books included. And then there are offline and mobile users.

The only way I can see to reliably support so many potential users and interfaces is to provide one interface they can all use. Provide one set of interfaces to the world so that those that can't use the tools and user interface you do provide have the opportunity to build their own. 

Of course you can still develop rich user interfaces for things like the iPhone and Facebook you just use this new programming interface to your main application to make it all tie together nicely. If there's a user interface you don't provide you're no longer obliged to provide it as long as you've explained clearly how someone else could. 

So that's my view on how to support the growing problem of multiple user interfaces