Another problem with that rule as applied to the coast is that e.g. 'to the right' of the east coast if you are flying Northwards covers the entire North Sea...
I exaggerate, but if I wanted to fly 1-2 miles off the coast, should I still have considered myself bound by that rule? Or only if flying within 0.5 nm of it? Or less? Where do you draw the line? (no pun intended)
Apart from that general ambiguity, I think part of the reason the rule was abandoned was that people using GPS nowadays sometimes follow the magenta line and, even if it happens to be on the 'wrong side' of a line feature, they still follow the GPS. Also, more importantly, people's faith in that rule may have given a false sense of security which was misplaced and abandoning the rule *should* mean that people's lookout *should* be better.
Fat chance.
B.