I have idea of new widget. xf:input is bound to instance node that contains html. Somebody probably wants to edit it by wysiwyg editor. I don't see right now good usecase though. So I'd like to see comments/votes/usecases. If control is actual then I guess we can support it.
You'll have the same issue here as in bug 316817. Input can only bind to simpleContent. I don't have a problem having a whole different widget, though. Maybe what we need is to come up with an interface that single node bound elements must implement (or more highly define our current one) and then we (or someone else) can start to develop 3rd party controls that aren't even really xforms based, but do allow for single node binding/nodeset binding. Which is really the only reason I can see for these custom widgets to live under xforms.