I am on holes so won't comment much - just a few things.
The colour vision requirement is an old thing, passed down from generation to generation of grey haired aviation regulators, without anybody really questioning it. Then
Pape came along and more or less demolished it. It's largely bogus.
The hearing (audiogram) requirement for the JAA IR is even more bogus. It isn't an ICAO requirement (no FAA ATP has got one, for example) and while the locals here like to pretend their hands were tied by ICAO, this is a disgraceful misrepresentation. ICAO merely recommends that an IR holder meets the same hearing requirements as a commercial pilot, but does not state what those should be. The morally and intellectually superior Europeans gold plated the ATP hearing requirements with the audiogram and then then pretended that ICAO forced them to do the same for the IR. This one is completely bogus.
The stupidity of these requirements is underlined by the fact that on
renewal medicals, JAA offers a
demonstrated capability route. This is of course necessary to prevent thousands of old and highly experienced ATPs losing their jobs - something which would be politically unacceptable. Many of these are too deaf to hold a social conversation (without a hearing aid) but are fine when flying.
Anybody allowing standard X on a renewal but requiring standard Y on initial is standing on totally bogus ground. Airline pilos are all flying on renewals
These requirements DO stop many private pilots acquiring the IR - because most pilots with the funds to fly IFR/airways are not 21 year old unemployed ATPL candidates. Most are older professional/business people and as one gets older one's hearing doesn't get better. It's easy to fail the audiogram yet have a perfect hearing while flying.
It's also easy to fail the CV test yet see all the colours required in flying. Lots of ATP candidates have been doing their initial medicals in places like Hungary...
Bose-x would be right if he said that ramming reduced medical requirements down the throats of the present regulators is politically very hard. But to say it is right to leave them as they are is just maintaining the present elitist approach, designed to separate men from sheep for no particular purpose.