Bookworm,
Well, my question was answered, they don't. I was specifically musing on the benefits/practicality of a unit that combines positions of both RNAV methods as the data is already available (assuming DME input) and it isn't rocket science to write some software to do divergence and tolerance checks just the way airliners do just without the IRS bit (pos by DME/DME, VOR/DME or GNSS). I would have thought such a thing would be very resilient and so as RNAV is requirement for most airways and if you have that level of resilience, then there is very little practical need to impose the carriage of an ADF unless your destination requires it...which not many do having DME and VORs within range. I suppose the need for the odd NDB approach is another thing until we get GNSS non-precision approaches approved. Surely would be a good thing to have anyway.
Just rambling and somewhat incoherent thoughts, my apologies
