It'd be nice to see horn volume tied to speedometer or outside noise level (maybe some already are?). After all it's meant to be a safety device not a device you can stick your ear next to comfortably in any scenario.

If you're going 70 and want to signal to the guy left of you to not merge into you "it's too loud for a pedestrian to safely stand right next to" isn't very relevant (in both perspectives). At the same time if you're going <5 mph on a comparatively quiet backed up street there is no reason it has to be the same volume as the first case.