darkspirit, right now the crash volumes on WebRender + X11 are not sufficiently high for me to be worried. It was very important in the early days when we were hitting panics and nullptrs everywhere. At the end of the day, the GPU process is a very nice bonus, but there do seem to be problems with it; I believe some of those bugs have been reproduced on GNOME, not just i3. We have never actually shipped that configuration, and I imagine more bugs would shake out if we did.
My biggest concern crash wise was the OOM + shmem issue, but with bug 1582954 having landed, we should no longer see those sorts of problems on Linux, and should follow the well trodden failure paths of Windows/Mac. For images, this means they don't appear instead of a content process crash.
I know Wayland has long been promised to be the future, but it does have momentum behind it. Various distro iterations have tried (or are) shipping it by default. We can't have the GPU process there, so we do need to achieve stability without it. We manage it on Mac, and we will need to do so on Linux.
We are committed to shipping WebRender everywhere, and for the first time in a very long time, that means Linux accelerated graphics is a priority. The GPU process just bails us out if we messed up, but now we are in a position to actually fix the bugs instead of asking users to live with them. At least that is my hope :).