TBH I'm very much out of the loop, I just assumed because everything DTG have put out before was a MSTS derivative this would be the same! Having read up a bit I see they're using UE4 which is a completely different bucket of monkeys, the 3D models for rolling stock should be importable to TSW if the authors so choose, but I imagine everything else would need redoing.
TSW seems to be very buggy at the moment but I'm glad to see the systems are simulated to a much deeper level and there's a proper timetable. I'll watch it with interest in the coming months, it seems to be a solidish foundation that needs polish.
I also saw it's nearly £30 for the bundle but what's the point when it'll soon be on sale for a tenner?