One of the reasons for the MULTICOM is that it kept things simple and standardised - viz 126.7 unless a promulgated CTAF (like in North America). No need to worry about FIA boundaries or being on the correct area freq, especially near a boundary.
The mention of "Multicom" and "North America" reminded me of where things went pear shaped in the half-baked attempt to introduce the same concept in Australia over a decade ago. (Do a search for "Multicom" on D&G and you'll see a number of threads on which the ensuing mayhem was discussed.)
If you haven't been following Dick's thread on the Canada forum, pop over there and you'll see that I've extracted some stuff from the Transport Canada equivalent of the Australian AIP.
You'll see that in Canada there's a single frequency for use outside controlled airspace, everywhere!
Everywhere ...... except ....
Everywhere except in the vicinity of an uncontrolled aerodrome. When in the vicinity of an uncontrolled aerodrome in Canada, you must use either the published frequency for that place or, if there's not a published frequency for that place, the default frequency.
Sound familiar? It should, but...
The difference is that the default frequency for use at any uncontrolled aerodrome for which a discrete frequency has not been published is
not the same as the single frequency for use outside controlled airspace. In Canada, the frequency for use outside controlled airspace is - drum roll ...- 126.7 - and the default frequency for use at uncontrolled aerodromes for which a discrete frequency has not been published is - drum roll ... 123.2.
The reason things went pear shaped in Australia is that the default frequency for use at uncontrolled aerodromes was
the same as the 'outside controlled airspace' frequency: 126.7. Mayhem on 126.7.
So....
Here's what needs to happen in Australia to introduce a fully-baked version of this system:
1. All broadcasts from aircraft that are both:
- (a) outside controlled airspace, and
- (b) outside the vicinity of places that are not marked on aeronautical charts,
must be made on 126.7.
2. All broadcasts in the vicinity of places that are marked on aeronautical charts but outside controlled airspace must be made on:
- (a) the frequency published for that place, or
- (b) the default frequency of xyz.q (which must
NOT be 126.7 or nearby control area frequency).