I would like the option to water cool, mainly to cut down on noise and heat inside the room.
I have come up with a very simple DIY system that should be bullet proof and easy for anyone to make.
However to make it possible the board layout would need to conform to some standard sizes.

The system I propose is an aluminum rectangle tube capped at both ends with a hose fitting welded at each end.
The boards to be held in place with 2 x square u bolts. The welded hose fittings and capping can be done by your local welder.

Most places stock the tube in 6 meter lengths so if boards are say 150 wide you could fit 40 boards on the one heat sink (prob not practical to do that long).  As you can have the tube any length it will be flexible solution.

I guess the feasibility of this idea depends on if on if burnin is willing to have a predetermined distance and size of mounting holes to suit a standard tube/u bolt configuration.