I think we can get bogged down in the "ADF enroute" argument without realising the "ADF in approaches" thing is not going to go away anyway.
I can see UK's peculiar ADF enroute requirement going away (it's hardly echoed elsewhere in JAA/EASA-land already) but I can't see the general requirement for an ADF to fly approaches in UK and Europe going away.
How can it??
There would have to be a general de-commissioning of NDBs in approaches, and what they be replaced with? Almost nobody is going to replace an NDB with a VOR because a VOR costs much more to install and run. GPS is the only option, and that will happen when it happens.........
So, the discussion of doing away with the ADF totally hinges on a wholesale adoption of GPS approaches at every airport that currently has an instrument approach involving an NDB. This is going to take many years, at best.
Unless one adopts the U.S. style which is to allow an IFR GPS to be used instead of ADF and DME, and I see no indication whatsoever of this being adopted anytime soon either.
(And, don't forget, not carrying an NDB/DME in the USA does limit your legal options when it comes to alternates.)
So, while I think mandatory ADF-enroute is totally stupid, I really cannot see the slightest chance of the ADF going away for approaches in Europe for many years - IF you want half decent IFR utility from your plane.
On top of this, Cirrus owners usually want to avoid the DME too. This is much less likely to go away than the ADF. DME isn't "mandatory" on all that many approaches in Europe but the alternatives are often not available. Radar is one alternative but IME is so often temporarily unavailable at the smaller destinations; all you need is an ATCO (who is qualified and paid extra to provide a radar service) to be off sick... Timing is another alternative but frankly, in some places that have serious terrain around, I would rather know exactly where I am.
When I used to fly long legs VFR over say France I used to use the ADF as an enroute backup for the GPS. This is just handy and I would not suggest it is essential, but it does illustrate that the ADF is not useless.