If support involves the implementation of new code ie it is a “new feature”, then they never have nor ever will announce future feature plans, as the owners of SketchUp have been publicly traded companies (and this would be legally “insider information”.)
If on the other hand, the “support” is wholly a function of the operating system, and applications are given access to a particular GPU in the set of GPUs available on the system, then it would be “transparent” to any application.
We are talking about Thunderbolt interface here ? I guess the question would be which is the faster interface, the one integrated by the CPU manufacturer or the Thunderbolt ? And if Thunderbolt is slower, would the external GPU’s faster features offset the slower integrated GPU ?
Sounds like someone needs to borrow one of these external GPUs and run a test.