I think that you have all missed one point that could cause confusion and discomfort for PPLs who are not familiar with RIABS (and why should they be familiar with a non standard practice?)
Students are taught that under the rules of the air, the lowest aircraft (at a non ATC field) has the right of way when landing.
So, taking the scenario given before, a PPL is on final and a fast moving aircraft flies underneath, making radio calls that are without meaning, then should s/he give way as the other aircraft now has the right of way.
Personally, I understand the RIAB, having flown out of North Weald for some years, but others have not/do not.
Your thoughts would be interesting.