Have you looked at http://pugs.kwiki.org/?KwidSynopsis
, which is what the Pugs project is using? Otherwise, yes, sure you can, invent/improve one, then go suggest it on p5p, then work to help implement it (after convincing everyone) ..
IMO, btw. XML sucks for this kind of thing, its much too easy to typo, and thus isnt good for handtyped docs at all. POD is nice and simple to use, if it makes the parsing harder, thats just tough, internals generally are more complex than externals, to support those simple externals.