The OP has made a good suggestion to an annoying OEM "feature" that obviously wont suit everyone but some might like the idea. TBH, the 99.9% comment indicates almost 100% of one person's opinion.
As for blaring horns - anyone who uses the horn after another driver has done something daft, actually has no real problem and is just displaying their annoyance. The person just cut up for real, has better things to do with steering and brakes than blasting on the horn.
I use my horn so rarely Id not be able to find the button is it was on my nose. So moving the awkward indicator cancel switch would probably be a great deal more useful. Even better would be a CanBus hack to do this electronically.