I was wondering if this feature should work without Simplygon or any similar reduction plugins.
Right now I don’t see some of the options in skeletalmesh rollouts.
Documentation doesn’t mention any plugins needed or features enabled.
To be clear here are options that are missing:
I wonder how they got that screenshot if there’s no Simplygon version for Unreal 4.20 yet.
Simplygon was updated and it can be installed to 4.20, now. It has to be enabled as a plugin in the project, but I still don’t see those settings. 
Even though it says
LogMeshReduction: Using SimplygonGridMeshReduction for automatic skeletal mesh reduction
in the output log.