It’s late 2018 and I don’t see this on their roadmap. This missing feature is a blocker for me for supporting mobile and low end desktop, as movable spotlights are a required feature of some game types and mechanics, and hackish material tricks don’t do the job properly.
Unfortunately, my guess is that they hope this issue goes away over time as hardware gets better. The Nintendo Switch itself uses UE4’s full, deferred renderer, so I don’t think they have much incentive to continue adding to ES3.1 given that mobile devices and IGP’s will eventually catch up to the Switch and beyond.