I will say that the Gimp 'core rewrite' has been a project in development since the early 2000's. I have never seen a clear design document explaining what this new core is suppose to achieve and for what uses Gimp expects to be used by professional level Artists workflows.
The last development that I was paying attention to was the decision to switch to GEGL for there core compositing and pixel engine. But it looked like it would simply be easier and probably better to start from scratch and build an entirely new software build around a 32bit image architecture rather then try and retrofit there 8bit custom build compositing system.
I will also note that they decided to invest there limited resources into upgrading the gui from GTK2 to GTK3 rather then focus that energy on the core. That shows rather skewed priority focus for a software that has some serious issues.