The name "WebRender" is unfortunate though. Things with a "Web" prefix - "Web Animations", "WebAssembly", "WebVR" - are typically cross-browser standards. This is just a new approach Firefox is using for rendering. It doesn't appear to be part of any standard.
I remember reading at some point that WebRender could actually be isolated relatively easily and then applied to basically any browser. That sort of already took place, going from Servo over into Gecko.
So, it might actually turn into somewhat of a pseudo-standard.
You send display lists to it over IPC, and it's easy enough to generate those from C++. It has a well defined API boundary, which makes it easy to use.
This is in stark contrast to the style engine in Servo which relies on memory representation to be fast. So integrating it requires very tight coupling of data structures.
Buggy graphics drivers are definitely a concern, not just for security but for stability. Specifically, graphics drivers crash. A lot. Simply moving GPU access to a separate process (which is common in modern browsers) means that a driver crash doesn't bring down any webpages, much less the whole browser; if done right you just get a flicker as the GPU process is restarted.
The name "WebRender" is unfortunate though. Things with a "Web" prefix - "Web Animations", "WebAssembly", "WebVR" - are typically cross-browser standards. This is just a new approach Firefox is using for rendering. It doesn't appear to be part of any standard.