Admittedly, I completely missed Sketchfab’s May announcement that they now support Screen Space Reflections (SSR), i.e. object reflections. What this means is that any model in their browser-based WebGL viewer can now be set to reflect items that exist within that model. A good example (that likely will heat up your computer a bit) is shown below:
This is of course pretty awesome, especially for architectural models, where windows can now reflect “correctly”. Previously, it was just possible to set surfaces to reflect the environment map and that was it. Mirrors typically looked a bit strange that way.
As you can see in the examples above and below, this is not a 100% accurately rendered reflection, but it is very, very good and immediately improves pretty much any model with reflections. I am completely blown away that it works even with more complex models. For example, the model above has 280k faces! And I made every one of them reflective.
Try it out for yourself (e.g. with my Sketchfab uploader extension for SketchUp).