I'm pretty sure that there will. still be some parts of the UK where having a Chademo as a backup might prove useful.
Or is CCS pretty much ubiquitous? (I've never really bothered to notice on public chargers as I reach for the Chademo...)
We are in a transition phase. Almost every location in the UK that has CHAdeMO also has CCS, however: some sites have for example 2x CHAdeMO and only 1x CCS; also, many of the CCS don't work properly. The DBT equipment in particular (very popular because it was cheap and also early into the market) is based on an original CHAdeMO-only design from Nissan, which has been bodged to have a CCS output as well, and they have shown to have severe problems with both compatibility and reliability. So until recently a car with CHAdeMO was much better off than one with CCS.
However, most new deployments are with better equipment, and we are beginning to see CCS-only locations - notably Ionity, with sites that have 4 or more units, CCS-only, and much higher power (comparable to Supercharger). So in another year or two CCS cars will be much better off than CHAdeMO ones; a few more years after that and CHAdeMO-only cars may become a liability if old dual-head equipment gets replaced with CCS-only.
Of course the ideal would be a car that supports both, and there's no major reason why Tesla shouldn't support both on the Model S while it retains the type2 socket. It is conceivable that the CCS-enabling upgrade takes away CHAdeMO capability, though I wouldn't expect it to - would be useful if anybody with a CCS-capable Model S can confirm whether it still accepts the CHAdeMO adapter.
Model 3 (EU version with native CCS) on the other hand is unlikely to ever support the old CHAdeMO adapter because the DC connection is on different pins (and it would have cost them expensive extra parts in the car to support it, which is why they upgraded all the supercharger stalls to two cables rather than fitting dual capability in the car). They could in theory make a dedicated CHAdeMO adapter (essentially, today's adapter with a different plug at the car end), but there's little motivation for them to do so and I would be very surprised if it ever happens. Model 3 in the US (with the proprietary chargeport) could support the existing CHAdeMO adapters, though it has taken so long that it may now never happen.
If a future bodywork refresh of the EU Model S gives it native CCS like the Model 3, then it's likely to also lose the support for the existing CHAdeMO adapter - though by the time it happens that will not be a great loss.
