There really hasn’t been much work on Zigbee so if it’s not supported now I’m not sure it’ll be supported in 4. On-the-other-hand, if it does work now it should definitely work in 4.
A new reply will get added to openHAB 4.0 Milestone Builds - #2 by Kai when the new milestone is released. A new thread will be created when 4.0 reaches release status.