The facility will remain, but I can't give you a firm guarantee that the actual API won't change slightly from time to time (we've been adding functionality to pages.xml pretty regularly). So I can't guarantee there will be no non-breaking changes, but I can promise that there will always be some way to do what you are trying to do.
Excellent, thanks. A minor API change I can handle.
A minor followup. Would it be possible to add a way of overriding an existing pages.xml definition for a view. At the moment the only entry point I could see was getPage() which always returns the existing metadata. Maybe something like Pages.newPage( viewId ) which will always return an empty Page and replace an existing cached entry?