Well, there's no major "rewrite" of avast! planned. Sure, some things will change in the future, but especially Web Shield is quite a new part, so there's no reason to rewrite it right now.
Of course, we would like to fix any possible errors that may be present... but if Vlk said he cannot see anything in the dump... it's not very likely at the moment (if it's an avast! problem at all).
As for the roadmap, I don't think there's any plan for avast! 5 yet. Certainly not this year, I'd say.