Jean Véronis has a post on Technologies du Langage on the difficulties facing the deaf, with reference to a programme on France Culture on the advantages of sign language. (In an extensive debate in the comments section the case is made for the benefits of mastering spoken French rather than relying on sign language.)
To take a somewhat Shavian/Queneauvian line, the real difficulty seems to lie in willed blindness to the realities of communication for society at large. (As so often, good old-fashioned structural anthropology has much to offer in throwing light on the matter.) A small percentage of the population are born with impaired hearing. An extremely large percentage of the population die with impaired hearing. Between birth and death there are all sorts of situations where neither spoken language nor the written word serves well as a means of communication: concerts, large parties, large restaurants, factories engaged in heavy manufacturing, engine rooms, helicopters (ah, Ronald Reagan, Ronald Reagan, President of the cupped ear and beating propellers, how you loved this refuge from an obnoxious press), war zones under heavy bombardment, noisy natural phenonema such as hurricanes, tornadoes, storms at sea...
Here's the interesting thing. I have no doubt that it takes years of hard work to master sign language. But then, it takes years of work to achieve functional literacy, and Western societies assign as a matter of course some 12 years of compulsory education to the mastery of the written word. (Note that, unlike the Romans, we do not see incompetence at public speaking as a scandalous mark of educational failure; most adults in our society are deplorable public speakers, but it is imperfect command of written communication, whether in reading ability or in spelling, punctuation and the correct construction of written sentences, that causes howls of outrage. (Lip service is paid to the importance of numeracy, yes, but that is a topic for another day.))
Now, no one is born knowing how to read and write. Illiteracy at birth is not pathologised; we accept that these are techniques that must be learnt. Illiteracy after about the age of 10 is pathologised: someone who cannot read or write is not socially functional, and enormous effort goes into ensuring that no one faces social exclusion through incompetence in this sphere. This is easier in some countries than others (I'm told there is no way to say 'How do you spell that?' in Korean, which has an exceptionally well-designed writing system).
In English- and French-speaking countries, on the other hand, it is considered perfectly acceptable to take up years of a child's time on cock-eyed spelling 'systems'. 'Gh' after a vowel has not been a velar fricative in English for some 400 years, but it would be a pity if our writing system did not honour the pronunciation of our ancestors.
Both Shaw and Queneau objected strongly to the opportunity cost of this nonsense; as Queneau once said, perhaps the time could be better spent on something else. Some of the time, one might argue, could be spent on insurance against the kind of social exclusion that faces those who experience hearing loss late in life. A hearing aid works badly in situations where there is a lot of background noise; it's very hard on older members of society for their participation in a conversation to be reduced to 'Eh?' 'Eh?' 'Eh?' We might be better off if we had a social convention permitting a mixture of spoken language and sign language in certain social situations, the sign component rising as speech became less workable as a means of communication. As some of the earlier examples suggest, there are circumstances where this might save lives -- where knowing how to sign 'There's another lifeboat on the lower deck' or 'A rescue helicopter is on its way, stay where you are' would be considerably more useful than the ability to spell words commemorating long-defunct velar fricatives.
Funnily enough, the group whose interests would be best served by this change of tack are precisely those least likely to favour it. 'In my young day we were taught how to spell' rivals 'Eh?' as a conversational gambit as school recedes into the distant past. So it goes.
Shaw, being Shaw, came up with a new alphabet which he thought would work much better than the one currently in use, with predictable success. If we all learnt the sign language for a few common emergencies I suppose it might catch on. (I don't know the sign language for 'Waiter, there's a fly in my soup,' but it would certainly come in handy.) Not likely, no, but as Sir Humphrey used to say, 'Anything's possible.'