I definitely get what you're saying. The forward-curved-banana handlepost on a Brompton, helps the fold, because it folds down to the outside (with curve concave inward). That would need to be looked at careful for other bikes to get it right, if folding to outside or inside, and which way the front fork is pointed with respect to the hinge orientation. I've pondered this for my bike, if I trade out the original handlepost, to get one with a clamshell top clamp or ability to use a modern clamp stem, for easy take-apart if packed tight for air travel. If I get it figured out, I'll post about it.

Does anyone make a long handlepost that adjusts for fore/aft tilt? Like perhaps akin to typical modern micro-adjust seatpost seat clamps, with small steps? That's a highly loaded part, the design might work. I can't think of other tilt adjustable designs that would hold up to the moment on a long handlepost. I'd say the double-clamp swing-style is easier, but for me, getting the flat bar set up right, and clip-on aero bars also set up right (high enough for comfort), and that should set me up for all conditions. I just emailed Profile Design, the 70mm risers/spacers that look perfect, they've told me are incompatible with both of my older bars, but I can't yet see why. I may need to use a sturdy double-clamp to raise only the aeros, which they also can't endorse, I think mostly because they don't make the part, the loading on the aeros is way less than on the flat bars.