The RhinoCommon SDK holds all pieces necessary for devs to create external plug-ins that can do proper UV map exports, including the devs of Datasmith.
Regarding glTF @Joshua_Kennedy has been working on the glTF exporter (and importer I think) started by @aske , dev talk on that plug-in appears to be happening in the thread glTF-BinExport.
You can find that plug-in through the Rhino Package manager (Tools > Package manager…, or the Rhino command _PackageManager.
Not sure what the current status is of UV support, but I’m sure @Joshua_Kennedy will be able to enlighten us.