This post has two goals:
1)create some overview for Houdini GLTF workflow
2)ask some questions/get feedback

Houdini has three ways to export GLTF files:

1. File - Export - GLTF...
   You can save file hierarchy, but not animation
   
2. ROP GLTF Output
   Saved single geometry, for animation you can save all data for each frame.
   You can pack final stream in the end, and apply animation. This saved object only ones and transform animation for him.
   What if I packed different streams separately? Different combination of merging animated and not animated streams (all animated too), or transform some packed geo (transform sop - group) produce instant disappearing program from my screen (crash when saving file) or damaged file (Animation sampler output accessor of count 24 expected. Found 47 ///This is for 24 frames of animation). if I apply materials it's more likely crash, but damaged file is 100%.
   
3. ROP GLTF Character Output
   Perfect for exporting skeleton animation. Can't work with packed geo
   

So what we have? I can separate geometry by packing or assign materials. I can apply transformation only for entire scene, or save geometry frame by frame. I can export some animated character.

But! What if you have characters, static and animated (simply transform) geo. ROP GLTF Character Output exports only skeleton, even export both static and animated geo it's a problem.
My solution is convert all this staff into skeleton animation. Create some singe bones + (for each)capture proximity, merge with character animation (if sexists) + reparenting.
It's works, but not super elegant solution (weights = more data written to file). But automated and not time consuming.

I suppose, for now, it's a maximum for GLTF in Houdini. We have some basic support for animation and object export. Same for materials, with only alpha blending mode but not double-sided parameter or something else. And duplicated texture when you save Ambient Occlusion as well.

Maybe someone have some advice for export complex scenes to GLTF