Egosoft just announced that X-Rebirth VR is in early access now.
Base for this standalone game will be X-Rebirth - Home of Light (which contains all addons).
However the VR game wont be compatible with the old savegames since the game environment had to be adjusted for VR stuff.
Also will this new version of the game be based on a new graphics engine (based on Vulcan).
This new graphics engine is supposed to be tested in X-Rebirth VR in order to make improvements and fixes until X4 will be released with the same graphics engine.
About X4 not much is known yet (except that they are working on it).