Its interesting. A few observations on what people are likely to be looking for just FYI.
There are some very nice generic tools like maptool (
RPTools - Home) which is a very good VTT with generalized macro capabilities. The only real issue being there are limits to how much 4e support you can bake into your macros. Recent versions have gone pretty far, but there are still things which are difficult or impossible to implement in maptool.
Personally, given that maptool really is a
very good VTT I'm more interested in enhancements to maptool, some more 4e specific offline tools that are cross platform (The DDI stuff being windows only is a show stopper frankly) and things like the skill challenge resolution tool.
Honestly it is of course impossible to compare your application as a VTT with what's out there without being able to try it out, but I'd really urge you to look at what maptool has in that department. It seems a shame to duplicate years of effort in that direction when really maptool is 95% of the way there in terms of core functionality and has 1000's of users contributing. Seems to me maybe some cooperation with the rptools guys would yield interesting results!