Hadn't seen that particular CAMM module, interesting. I am less pleased by that, but cooling the front side sufficiently should also take care of that. You could also do thermal pads between the motherboard and those memory chips for additional surface contact.
Not really how cooling solutions should be looked at.
You certainly get better GPU memory temperatures from a GPU waterblock than without, so not sure why you think it would dump heat into the memory. The water isn't going to ever get that hot and will always take heat away from heat sources. Similarly the motherboard stays cool relative to power using components, so there is always a heatsink effect, and again if the main heat sources are cooled, that heat will also be drawn away from the board.
Not saying DIMMs should go away. This is just another option that I think has some benefits to they way I might build a system.
I don't really go in much for the RGB and displays. Just saying that that is exactly what some of these companies are going to be looking at doing. Being able to charge an extra $200 for yet another display on a motherboard will please them to no end.