Of course though, why invent the wheel twice?
It's cheaper, albeit somewhat slower to innovate (due to all the bugs and limitations) than if they had just wrote a new engine completely from scratch (because then they would really know what is going on inside and debugging probably wouldn't be so tedious).
This thread actually makes it seem like they really did just take portions of the old engine, updated a few things and then split it into modules.
A bit like Apple really; no inventions, just cramming the best together and adding an "i" to the name and slapping on an outrageous price and calling it revolutionary.
Although I am very optimistic for BoM because many patches back, I had decent performance after finally figuring out the best settings for my rig
My advice to everybody on here:
"Be a pessimist, and expect the worst because then life can only get better."