v2 will be a complete rewrite, which will require new addons. There is a plan to possibly offer a legacy template addon, which will allow you to use old-school templates & template tags, rather than the new fancy way. The only similarity between v1 and v2 is the name "Pixelpost", other than that, they are completely different animals. But providing everything goes as planned, addons for v2 should be much easier, and faster for both the users and the developers.
One thing I can tell you about v2 though, it has very sweet mod_rewrite support built in, if I must say so myself.