Vs a single tag to embed a model. 3D models are complicated. If the <model> element is complex enough to support anything the user decides to embed then it'll

Vs a single tag to embed a model. 3D models are complicated. If the <model> element is complex enough to support anything the user decides to embed then it'll put a huge burden on browser developers. That's fine for Apple and Google, but it'd be another nail in Firefox's coffin. On the other hand, if the element only supports (say) the gltf spec then it won't be a simple case of adding a model for a non-technical user. They'd need to export or convert their model, textures, shaders, animations, etc. 3D support is probably an order of magnitude harder than video. And video is hard enough.