I haven't actually purchased calipers yet (or anything else on my list besides the frameset, rims, hubs, and groupset) so I may still change my mind but...

1. Campy groupset was a must
2. There is no hydraulic Campy groupset yet
3. I also picked a flat mount disc caliper frame
4. There is no flat mount, hybrid hydraulic caliper option right now (HY/RD is post mount-only), but TRP did just introduce the slightly lighter Spyre SLC flat mount caliper that I plan to use
5. I'm being a bit of a weight weenie (see above comment), so even if there was a hybrid hydraulic, or even full hydraulic option, I'd likely still stick with the full mechanical setup. It's worked well enough for me for years (Avid BB7 front only on my commuter/cross bike) so with front and rear discs, a lighter overall bike, and no commuting load, I believe I'll be perfectly satisfied with the braking.

Time will tell, of course, and if next year there is some amazing full-hydro, lightweight (and not ugly as sin as most hydro levers are these days) Campy option available, I might just have to suck it up and upgrade my bike to it. Shame