What do you want in a custom ROM or kernel to do?
Custom ROMs or kernels are not automatically better than the stock kernels. The developers at Motorola, or HTC or Samsung for that matter are not bad developers and actually have full access to the hardware specifications in these devices. I'm not taking anything away from the guys who put together these custom peices of software, but I think they'd agree that they're working at a disadvantage when compared to the engineers who actually work for the maker. There's a reason why things are often weird when running a custom ROM.
The main reason you are not seeing a bunch of custom roms is Moto has kept things pretty vanilla, but added some features like active notifications and touchless control. They haven't done what samsung or HTC has done where they pretty much re-work the face of the OS. The reason I have flashed any custom roms in the past is to get updated versions of android before officially offered, or to go to an AOSP ROM. I feel that I would actually lose out by running CM on this phone. On other phones there were trade-offs, losing the camera app or some applications tied to the framework, but on this, I don't see the benefits like I did with the S3 or HTC phones I owned before it.