The faster SL moves away from OpenGL the better, and this is a solid step in the right direction.
Even older and midrange PCs will benefit from this in the long run. SL in its current state simply cannot properly utilize modern hardware. They cannot continue to take the minspec approach and expect it to stay alive.
If they continue along this path and get us into Direct X 11/12 or even Vulkan than people will see an explosion in performance. Yes this new client update is going to demand more resources, but the people quitting because they can no longer use their rigs from 12 years ago are just being unreasonable. Imagine running SL at max settings at a solid 144 FPS because it can finally use all of your CPUs cores, yes please.
PBR is a basic feature that has been an industry standard for a really long time, it allows us to create more immersive and realistic spaces, isn't that the entire point of Second Life? To create virtual worlds we can feel immersed in? I'm not going to sit here and pretend that these releases haven't been a little rocky, and yes the Firestorm client in particular needs some work, but being anti PBR/New lighting engine in general is just silly in my opinion.