No porting is needed, i am using apps there i was running on AS 3.5, then 4.0. Some API changed but mostly old Tcl API is the same, we just have many new commands.
Naviserver is fork of AS 4.0.11 but this year we ported some stuff from AS 4.5, mostly pools, tasks, new ns_http command but NS has new ns_https/lightweight nsssl module.
As for seriousness, Zoran relies its business on it, i am using it as swiss knife and actually at my new company we are using it for backend/server parts, i am not sure how Stephen relies on it. And, this is opensource project, we do not have many commiters but this is because of lack of popularity, we never intended to fight for aolserver developers or lure them from AS.