[xpl]

> You can't cache it at every resolution

True, but you don't need everything at max resolution simultaneously, so you can update your caches according to the current zoom level and thus get infinite zooming if you want.

At a large zoom level, few things get into the viewport, so it shouldn't cause troubles. My guess is that the troublesome scenario is when you zoom out (so that lots of pages can get rendered simultaneously), not when you zoom in?