The Grand 4 has never been hinted at by Steinberg. If it’s released anytime soon it will be a total surprise. The closest we’ve gotten to a TG4 is the two new pianos that were recently included with Halion 6 and Halion Sonic 3.
On the VST front, we know that they’re working on Halion expansions and a Halion-based FM synthesizer. They’ve also hinted at the possibility of a new version of Steinberg Virtual Guitarist and Virtual Bassist.