Dick
I am pleased to be in general agreement with your thoughts.
The 8 minute call is however an excellent idea for warning others of high speed RPT arrival. The 10 Nm is a legacy of CTAF boundaries and is not valuable as one is far more interested in the time everyone will be mingling in the circuit than trying to calculate that from a distance and aircraft type.
As well, the difference in IFR and VFR charts means different flight rules will be calling on different CTAF en route - and VFR will be off the area frequency more often (when IFR are not) thus reducing situational awareness.