3dsMax developer has changed their delivery model to continuous delivery. Instead of delivering a feature at one release, now a feature will be delivered continuously until all the planned feature is finished. The automatic OSL > HLSL conversion for viewport was the one of them. It has been improved in every PU since tisinception. Now almost all OSL shader will be automatically converted to HLSL including 3rd party OSL shaders.
Also, the viewport playback performance of animated OSL map has been greatly improved.
This is the viewport playback of the sample file for my OSL shader pack1 in 3dsMax 2019/2020.