This is more of what I explored regarding lightmaps and AO and thought-dump and suggestion.
I looked into Marmoset Toolbag and Blender for baked lightmaps, Marmoset Toolbag's baking seems to me to be about converting high-poly objects to low-poly objects with good materials so that the low poly object has a good look even though it has less detail. Also it doesn't produce a lightmap, but it produces Ambient Occulusion. Its mostly about making models look great, not about the game map with baked lighting. I don't see anywhere to bake lightmaps.
For Blender however, it it able to produce Ambient Occulusion and Shadow, I have not yet tried to bring Shadow into playcanvas as a lightmap yet, I guess Shadow is equivalent to playcanvas lightmap and will attempt later today.
I followed this tutorial which produces baked shadows and textures https://www.youtube.com/watch?v=LL5QiLspUvY
I'm primarily a programmer (Java/Scala preference), so from a programmers perspective I can see that Blender can be scripted and that blender files can be created programmatically http://homac.cakelab.org/projects/JavaBlend/. Then it occurs to me that better baking of lightmaps could be done by writing a program which passed the PlayCanvas 3D data through blender by creating a blender file, then starting blender with a script and bake lightmap and then use the output images as the lightmap data.
Such a program would have positives and negatives.
1. Positive, makes realistic lightmaps and ambient occulusion from PlayCanvas models and lighting and outputs those as images. The layout of the model would then determine the lighting in a realistic way and you could get images looking like your above.
2. Negative, slow as it needs to take time and CPU/GPU to produce, expensive in compute time and therefore un-attractive on server side due to cost. A GPU solution on a powerful GPU card could be faster? but cost.
3. Negative, slow is boring for user to wait for the render.
4. Negative, not really a lot of users asking for this I assume.
5. Could be made faster by only specifying certain objects to participate in the 3D data for bake, user should minimize the number of objects involved, this could be a "High detail lightmap bake" feature, if you checked it, you get a high detail lightmap.
6. Positive, quite spectacular in game/model, allow for model to be created programmatically and then the lightmap to be generated at runtime, ah but sad, it takes some time to generate. Would be nice at runtime though.
So its not particularly unusual to use Blender on server side in a scripted way. Although they don't do realistic PBR rendering in browser (yet), they ask users to pay for renderings which I guess they use Blender for rendering and storage of models. You could imagine that realistic PBR in browser could be done if their data was passed through your system.
Well since your PlayCanvas is all scripted I could do it myself right? I don't see any barrier to that, its a sequence, get the 3D data (have that in runtime when the model runs), send it to my server, convert to blender, pass through blender and generate lightmaps, save lightmap images, server delivers lightmap images to client playcanvas, done. That could be a open source project I could try to make if I can get time in the near future. Certainty in the simple case of just a few Cubic objects its not complicated.