So a question looking at the rear of your case, it appears that there is a 1U 19" RM slot between the PSU mount sections and the motherboard divider plate. Is this unobstructed in the case on the PSU side? I realize that I'm unlikely to ever decide that I need a TX10 in addition to my M8, but that's really interesting. I knew you could get multiple RM slots in a top configuration but never really looked at the TX10-V (always the 'D') so didn't realize there was another possibility.
Thinking that would make one heck of a monster media server case - with 16 port switch built right in...
Yes, it is unobstructed unless you buy the optional PSU support which juts into the space a little bit. I have two of those support for my dual PSUs. That little corner is another option for hiding cables in addition to the 4" space between the motherboard side and the PSU side of the case.
"I'm gonna speculate it will be your last build as well." ... I'm tempted to say that, but I'll probably end up like you with multiple builds; but I do not anticipate that "multiple" would mean very many for me. I'm devoting effort to make this one a good build and merely upgrade it as necessary. In terms of time, effort, and thinking, these builds really are challenging, not to mention cost. But I absolutely love it and I'm happy I started the project. I do not consider myself the ignoramus I used to be with respect to computers anymore. I've learnt quite a bit.