SNDS

What I suspected at first was a kind of signal redundancy, as he used the internal DP injection port, despite the back I/O has a separate one, but your idea seems more legit

The solution Linus is talking about (considering it is a cable of some length and uses Thunderbolt 3) is likely the upcoming Corning Optical Thunderbolt 3 cables that are supposed to come out soon-ish (The manufacturer in the link is Sonnet, but the cables are likely based on Corning tech). They propose the ability to send Thunderbolt 3 signals to a run of around 50 meters (~146 ft) or more. So while Linus cannot talk about it openly yet, they have been announced. It's just a matter of when. 

https://appleinsider.com/articles/19/09/11/long-optical-thunderbolt-3-cables-are-coming-soon

I highly doubt that will be anytime soon. He has had this solution for multiple years now. And if he hasn't told us to this day it is weird.
I think it is an engineering sample or something from Intel (they made thunderbolt) and they never got the technology working (mass production, reliability etc).
 

Please let us know as soon as you can about the "secret sauce". I have the same Caldit Thunderbolt 3 dock and am limited to 2m. Can't wait to see the longer solution. 

From what I can tell, the custom 20-pin and 24-pin hook up split off to all the various molex connectors. I'll try and remove the backplanes and send a few pictures for follow up. The concern I have about the backplanes is drive compatibility, Backblaze noted in a few of the articles regarding their open source plans that the backplanes and sata cards are finicky and seemingly only support a certain set of drives and is firmware dependent. I'm hoping this ends up not being the case. That said, I'll do some testing once I can hook up my monitor and setup Unraid. I'm hoping compatibility isn't a big deal with Unraid and the hardware will play nice.

Have to start somewhere.
 
Best way to learn ?.
 
What's the case? Don't think I can help much here without knowing what we are dealing with. Million pictures would also help, just around how the drives mount currently.
 
As to backplanes I have the opposite opinion on this compared to 45 drives but that said I haven't used cheap ones and thus never had one fail. So I guess it's a bit of siutation matters. Direct cabling for you is going to be easier, that's my gut feel and is typically true when making modifications to cases.
 
It'll be much easier to use SAS cards at it's cross compatible and supports expanders where SATA often does not as it's an optional feature. Lots of cheap SAS HBAs on ebay, something like an LSI 9211-8i IT mode. If you want less HBA cards bump up to a 16i model card.
 
Pretty sure a dual PSU Y split cable will work here, photo would also help here too. Modify pin outs if necessary, simple to do.
 
Note: Missed your link to photos while typing until I got to the end. If you can get them posted in the thread that would be nice though.