Well the main issue,as you pointed out, is not so much about implementation in UE4 as it’s more of a case of a lack of any kind of standardization from with in the DCC type application and the lack of any software developer willing to adopted edit features that are unique to the application using someone else technology.
A good example is hardware based physics in UE4 is trapped in CPU bound rendering due to incompatibilities between ATI and Nvidia.
Second issue is the problem of Patent ownership as to who owns what formats and more important what the terms and conditions are covered under license even as being open sourced.
Granted USD/USDZ is covered under open source but what licensing format? MIT/CC)? If GPL game over as GPL is “not” compatible with GPL and is excluded.
Does the technology allow for interactive licensing? Interesting is that some application license excluded interactive use and 3d printing.
Sounds simple as from the tip of the iceberg perspective.
[100% opinion mode]
Just to be sure that we are on the same page we are talking about ?Meet the Experts: Pixar Animation Studios, The OpenSubdiv Project - YouTube
As a "game"engine Unreal 4 has taken a different direction by providing tools built into the edit environment that will take advantage of 3rd party applications that has been using advanced pipeline technology with out the need to reinvent the wheel but at the same time Epic is creating the path as UE4 being the final destination. The need for UE4 is to put into place the nuts and bolts by which other products can be “plugged in” and more than a few features have been add over time that really makes no sense until you look at iit all from the frame building perspective.
Two products which are very interesting is Unreal Studio and DataSmith, which is in Beta at the moment, where 3rd party formats that are questionable as an addition to the main UE4 product could be added to the pipeline into UE4 as to questionable fair use rights.
As I said I’m guessing but what is fact since 2013 OpenSubDiv, like all things software based, suffers from a case of obsolesce by design and the up-scaling of hardware solutions like GPU and CPU as well as run time optimization in UE4.
Sorry if I’m off the path but I really don’t see the value of adding run time sub division to a real time rendering environment that would be best done with in the DCC pipeline.