Revamped lighting and shaders, i think thats the main, i mean, i know they added shadows which is good ofcourse but for example i wanted to light a level...

flat shaded surfaces+lights+dynamic shadows alone wont give a great overall look, this is assuming youre using blocks and not models

If you do go the models route, then you get shadows+shaders and you lose lighting[except sun], unless ofcourse you bake, which is another thing that increases dev time.

We paused scion because of this problem, will resume when we have a secure and decent level lighting pipeline

Ofcourse this limit also depends on the game youre undertaking, not all games need alot of local lights, sun light is enough sometimes..

I think when someone hears of an engine update, the first thing that comes to their minds is better visual/immeditate speed increase...