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have you thought about running a kickstarter campaign for this case first? as i believe having a successful campaign can make it way easier to get your case a large scale manufacture! I guess even protocase will be more than suitable for the campaign and you'll just have to sort out you sli bridges or nvlink! along with power supply and special PCIe riser cable. This is a very fail-safe plan and I'm more than sure it will succeed profiting you and the project a lot! plus your time to market will be a lot less if finding manufacturers is being a bottleneck. I'm sure you know best! all the best!
