Currently I'm planning to mostly add to it, things like achievements, global high-scores, more levels, etc. to test the tech.

Maybe make other small games, I've noticed I tend to get swamped by the need for art in larger projects (sprites, textures, models, music...), placeholders graphics only go so far, and I'm just not time-efficient at doing any kind of art myself, quick PaintShop hacks are okay, but anything more complex and I'm doomed ;-)

3D may or may not be too far removed, it'll depend on how fast the W3C settles on a 3D standard (be it WebGL or something else).