What you mean is that your setup is too specific?
What about using more common part like apogee drive or predator, even if it's little bit bigger
The thing is that it won't just be a little bit bigger it will be a lot bigger. The minimum size would be a little over the size of @iFreilicht Brevis case, just imagine a 1U Waterblock with a regular EKWB waterblock on the GPU and replace the PSU with a Radiator in there.
You'd still need space for a reservoir and pump, or going AIO style without a reservoir and use an Asetek type CPU cooler+pump combo and a HDPlex board would need to go somewhere.
Even if your case/block is limited to a very specific set of hardware, so is the Zotac, and they apparently think they can sell enough units even at that high price to justify R&D and marketing.
Broad hardware compatibility comes at the expense of size, so it's a tradeoff.
You are right, but in order to get that all worked out properly I'd need to invest another 1000+ dollar for a new prototype that has all the changes and right now I don't have the option to make that commitment.
This small talk really makes me itch to do it though