Now, my idea of this setup is:
Cards with heatsinks on, vents and plastics off.
Vents will be present, but not stock ones, I will invest little money in hi-flow 220V 120x120x38 vents and hopefully, they will do it.
Cards will be submerged in mineral oil, case and pumps are going to be defined, radiator and vent for him also.
Cards will be popped in oil upside down, with pcie slots up, extenders going above to motherboard.
I have seen a lot of air resporators running in these cases, also doing good oil circulation, maybe they could replace vents in some case?
I think not... better to keep 120/38 vents...
In next few months will be done I hope.
Case material sould be:
1) Glass joined with silicone (maybe could break in case of too hot oil?)
2) Big plastic tubs (plastic+oil+heat=?)
3) Metal tubs (not great idea, ergh...)