If you put a pivot in the head tube area, around top tube height, and then put a curved slot below it, around down tube height, and had the actual head tube as a separate bit, with some sort of fastener (something along the lines of a qr skewer) to go through the frame and head tube in the curved slot, you could adjust the head angle.

People are prepared to adjust fork lengths before climbing and descending, so why not head angles, which IMO makes a bigger difference?

Has this been done before? Is there any big problems with it I haven’t considered?

Would it be completely infeasible without adding loads of weight because of the amount of force the head tube area is under?

No one?

It’s a good question.

I can’t think of any recent frame like that. I suspect any are more likely to be one-offs for prototyping purposes.

Can you imagine the arguments it’d create here?