A 4.0 release has been delayed for many reasons, including the formation of the ACT, documenting what we have, and coding for 3.5 and now 3.6. Those actions are largely in response to community requests.
The AOLserver code base is *already* forked. There are at least a half-dozen distributions available, causing untold confusion for new users. (Yes, I am part of the problem. The distribution OpenACS is currently recommending is missing numerous bugfixes and features, and has no clear maintainer(s). I think a revived OpenNSD would probably meet a similar fate. There are lots of good things happening in the SourceForge tree, let's focus our efforts on integration instead of further division!