Hi! I'm kinda new here but have used a variety of game engines, mostly as an artist but sometimes as a scripter.
Whilst adding shader support is all well and good, I find that hobbyist game developers can work better with what (I suppose...) could be called "Effects".
For example, the shadowmap idea, defining regions where a 3D actor is in light or shade is brilliant and anyone could use it.
Full scene tonemapping with exposure control and bloom to allow the lighting of a pre-rendered scene to have an element of nature.
Even, dare I say it, Normal and Specular mapping on 3D actors.
These both allow better integration between the 2D and 3D elements of a scene, and honestly I think that should be paramount. This is a 2.5D engine, and I reckon it should be the best one it can be.
So, In conclusion, those who desperately want shaders will probably have the wherewithal and manpower to code them in themselves, access to shaders does not mean they will be easy to use or implement (I know that from experience, thank you Quest3D!), the rest of us would probably benefit from some solid "effects".
But anyway, thats just my opinion...