Apologies if this is resurrecting an old thread. Seeing as I'm finally back and able to upload again, I've been thinking of a few improvements you guys could possibly look at IF you epic folks aren't already working on them. I'm aware that you guys are working hard on getting sketchfab to work as best as you can, so none of these is a must, but merely just suggestions
Enable the user to be able to turn off shadow casting on any model. This could help in making sure things like particle effects, Custom Sky Dome Meshes or effects like light shafts etc don't cast shadows, or at the very least, allow for more possibilities of using lights that cast shadows.
Super excited to see animation is getting implemented, with that I'd like to know if it would be possible to somehow implement a sort of motion blur filter on models, not necessarily something that overlays the camera but rather a sort of "per-model" motion blur effect. Haven't worked with animations in sketchfab myself, but noticed from those who have uploaded animations there isn't something like this to make the animations appear more fluid.
Always face camera
I've been running across a few situations where I thought it would be quite handy to have a model or "sprite" having a setting to "always face camera". This could be useful for plane effects like flares, explosions and small debris.
With the recent implementation of PBR, I've been thinking about something could possibly improve reflection quality of models if they are part of a scene that has a few models surrounding them. Would it be possible to implement real-time reflections into PBR, maybe have a setting that could regulate the quality of the real-time reflections, and mix the reflection value with the roughness/metallic values. If this is on the road map already, apologies.
Displacement mapping / Parallax Mapping
Now from a game engine point of view, both effects are quite good, though parallax mapping isn't an easy shader to implement or one that would be very performance friendly for lower end graphics cards, though I do believe it would be nice to have any of these effects in sketchfab. This could keep polygons at a minimum, and still be able to get detailed quality from its surface. Normal Parallax mapping would be definitely a step up, occlusion parallax mapping is a lot more intense on hardware, so that might not necessarily be a good idea to use IF parallax is added. xD
Camera Lens Effects / Bokeh
With the additions of bloom, chromatic aberration and all the other awesome effects, I've been thinking of how one could make these effect such as bloom look in some cases more realistic. Would it be possible to add a camera filter for Lens Dirt / Bokeh?
This can be especially useful on something like a jet engine's jet blast, or the bright glow effect from lights that face the camera almost directly.The filter can be regulated with a threshold / radius and brightness value that could ensure that the effect can be customized to fit the user's scene.
For example, like this effect on the camera.
This would likely fall with Displacement, however this effect could be useful for something like water, glass or heat distortion effects for something like jet engines or lava, to make them appear more realistic. Ultimately something like a normal map could effect the amount in which the distortion effect takes places.
This could go together with general camera filters. As with the Lens Dirt, the flare could be adjusted according to threshold, size of the flare and brightness of the flare. Models that glow would definitely look a lot nicer with this sort of effect available, especially on things like car headlights, street lamps, jet engines, and objects that have an emission color to them. if however this filter could be added, it could be even nicer to be able to upload a custom lens flare texture with a black background to be used.