It might be just my preference, but I always added this kind of functionality using macros in MoinMoin -- sure, it's a little more awkaward to type {{{<<<Link Page|Text|Extension|Extension>>>}}}, but you have a generic mechanism for extending that's guaranteed to not collide with anything.

If you extend the links, then soon you will have to extend tables (to allow styling them), headings, blocks of preformatted text (for syntax coloring), etc. -- and what was a well-known, standard markup becomes some complicated replacement for HTML.

-- RadomirDopieralski, 2007-02-26