For race oriented frames, I really like the features of the recent Cannondale SuperX tick a lot of boxes of what a modern gravelracer should be like. Not saying it should have the same look.
Slighlty modifiying Pat's list:
1. T47 or BSA bottom bracket
2. Clearance for 50c tires
3. D-shaped seatpost for more compliance
4. UDH
5. Sufficient chainring clearance. (46t single, 50t double)
5. Aero looking, it needs to look fast
6. Miminal mounts, or at least the option to have to have a fork without bolts
7. FSA headset standard
8. Lightweight (doesn't need to be sub 900, but rather close to 1000g than 1200gr for the small frames.
9. Frame/Bottom bracket stiffness and compliance: accelerating should feel like a road bike, but still should have compliance i.e. trhough features like thin seat stays, D-shaped seatpost.