What was the main learning you got from building the engine? Was there some feature you wanted that no other engine at the time had? If you built an engine today, what would you do differently?
For a modern engine today - I think the architecture of the engine would look different - and would focus more on creating and organizing content then mostly on rendering.
Todays graphics engine look completely different than the first flexibel pipelines around 2002-2005, and the rise of AI for usage during rendering will change the tech paradigms further (for the younger ones: In 2001, NVidia announced the Geforce1, we had 1 pixel shader and 1 vertex shader :-D LOL)