Another opinion.
As far as I know I’ve only known a few people who have ever used a “game engine” for ArchVis purposes and I’m more or less sure that Epic never even consider this as a need that goes beyond UE4 being just another engine for playing games. Personally what I have found is UE4 does not place hard coded restrictions based on what’s consider best practices as to what would be considered reasonable as to things like poly counts or material resolutions so as far as archvis goes it’s really an innovation as to the need for real time rendering which has always been in demand by the CG community in general.
By removing hard coded restrictions has created the undiscovered possibilities along the same line that motion capture did not replace the animator but in fact increased the popularity of animations as well as jobs in the process.
On the surface EU4 is just another 3d application equal in possibilities as programs as Maya or 3ds Max but with a real time rendering and movement system that is not available in flagship applications designed to just get the single frame renderer. This need could be why Autodesk is introducing Sting Ray to fill the gap.
Overall though it’s to soon to state facts in favor of speculation but based on how UE4 continues to improve with every release, integrates well with most if not all applications that support the FBX pipeline, I can see a bunch of kids working out of their garage producing a full length animated feature film that would give Pixar a run for their money.
As for selling ArchVis to a company most do their work using CAD systems using mico measurements equal to real world objects as to function and form that translate directly to archvis rendering so there has never been a market for off the shelf products.