Another bad idea. Technically astute enthusiasts understand the very real liability of CPU/GPU water leaks that can damage PC hardware and thus avoid these closed loop cooling systems like the plague.
It really is not a bad idea because anyone who would buy this would be sufficiently very tech savvy to start with.
I don't see non-enthusiasts even daring to experiment with such things. So as long they know what they are doing and dealing with it all good. They are very paranoid in checking for leaks on a regular basis.
What do you have underneath the GPU in your system?
But on a more serious note - a closed loop CPU cooler can be made to fit on a GPU just fine. Even with the need for tinkering or ordering a bracket and possibly some additional heatsinks the cost will be substantially lower than what AC Hybrid costs.