This may probably not mean much coming from a noname like me, but I think the whole idea has something really revolutionary and I'd supporting it as good as I could.
There is one problem I see with it however. If I got you right, then the maps as you described them would be primarily layed out for a Zelda-esque perspective and gameplay. However, since the outcome relies on the interpretion of whatever program loads the "map", one could easily transform the thing to a platformer environment or even something completely else alltogether.
So, while I happily browse the web with my Zelda-esque interpreter, I'd suddenly stumble across a map that'd be build with a plaftformer interpreter in mind, and would thus essential f* up my Zelda interpreter. Or at least make the map an unplayable mess.
Of course, this works the other way around, too. If platforming would be the main idea behind the maps, the Zelda interpreters would get problems.
If the maps are hosted on normal webservers, though, I can already see the Firefox plugins coming
"The content of this page requires an additional Plugin for viewing"