Yes, I can confirm that custom shaders are possible in Toolbag. You can view example shaders in the Toolbag install directory. Multiple detail maps are not currently supported but this is something that should be possible with a custom shader. @Axi5 we use human-readable code so it's easy for users to see how they work and…
Thank you @EarthQuake for the link! @Axi5 A 4K map isn't comparable to multiple detail maps because it won't be able to capture the very tiny crevices in the skin. This subtlety is important in order to create more believable skin and in turn cross the uncanny valley. It does not have to be implemented in all objects, so…
@Axi5 It is possible to make custom shaders for Toolbag, I think, because there's a folder for custom materials somewhere in the installation folder. If it is possible to do this in the softwares you just mentioned, then how come no one is doing it? Or maybe I just haven't encountered one yet. But still, you'd think big…