The Co-Axial escapement is an Omega thing. Sure, it was invented by an Englishman, but when you see a Co-Axial Omega 2500, you know that while it may have started life as an ETA 2892, it's not available in any non-Omega watches. The 8500 is just a further step away from standard movements for Omega. It also, like the 3135, has a two point bridge, instead of the single-point used in ETA movements.
Bold move, gorgeous movement. I want.
ps. I suppose it has two barrels so it can run at 28,800 without running out of steam, unlike the 2500 which is slowed to 25,200.