Oh this is sick, thanks. I have that same ultegra deraileur, but might try the deore first.
Re discs, no idea, guess I'll find out. I thought it was the same rules as with rim calipers? Road disc calipers = short pull, so that's fine for drop levers?
It is the Hubbub alternate cable routing, if I remember correctly. Should work, never tried, without that the 0.3 difference is a bit too much I think.
https://hubbub.bike/hubbubs-original-shimergo-solution/
Looks great, and Shimergo on this bike feels just right. How would it go with discs, though? (I'm probably overlooking something.)