I was recently looking into @zeux's work on https://github.com/zeux/meshoptimizer/
this is mind blowing compression tool

I can confirm that normal gltfpack compression with "KHR_mesh_quantization" works Model Viewer 0.10.0

but when I compressed the model with meshoptimizer codecs (-c) it didn't work on Model Viewer 0.10.0

I got

GLTFLoader.js:267 THREE.GLTFLoader: Unknown extension "MESHOPT_compression".

So ya it would be great to see this added to model viewer

A little how to is also mentioned here https://github.com/zeux/meshoptimizer/tree/master/gltf

this is the size I got when I did the compression

Thanks :)