All right you guys.
Been a nice long summer vacation but i have not forgotten about this project. Quite the contrary - it is rolling along nicely, with some modifications along the way.
After deliberating with myself for a long while i finally gathered my financial and mental strength to order a custom-geo titanium frame from XACD in Taiwan. It was a lot of fun to fiddle around with. Their service was excellent and i even got a little custom badge on it for fun. It's prettty much the same frame as pictured earlier in the thread, but a slightly different fork (not pictured).

They finished building it this week and just shipped it so not long left to wait now. In the meantime, virtually all parts are in place. Some slight changes to accomodate the frame have been made. I think i will also go for a GRX 1x12 setup instead of the 1x11, for sake of "up-speccing" the bike a little bit. That'll prompt a new chain and cassette, but i'll just throw the 11spd stuff on another build.
I expect i will still need to fiddle with things like seat tube clamps, headsets and such so it might take a month for extra parts to come along once it is recieved, but for what it's worth almost every part has been sourced.
As for wheels, i ended up getting the slightly janky Meroca wheels pictured earlier, which in fact had some beautiful aluminium 27'5" rims. Gonna have to re-spoke them for oilslick spokes somewhere down the line. I put an order in for some janky carbon rims in supposed oilslick that never arrived, so there's still a big gaping hole in the 28" wheel department. Guess i will keep looking.