Lighting is an issue, but in the long run I suspect it’s going to be the lack of fully multithreaded game code that’s going to hold the engine back when compared to what Ubi Soft, Rockstar & EA have up their sleeve - that’s really going to help with dynamic, densely populated worlds and fast streaming.
And as for AAA Devs, AAA Devs were heavily customising UE3 throughout its lifespan. and it’ss going to be pretty easy for big devs to add their own lighting solutions pretty quickly now that PBR is standardized across the industry.