Been thinking about this, and don't really see why they have opted for an exclusive model when that option has been resoundingly rejected in the past for other implementations of new gear.
NAV/AUSEP, RNP & RVSM were all introduced and those that didn't have it were (are) massive roadblocks in the sky, that reduced to insignificance in time. I think the approach made with RVSM makes the most sense, all can enter, but the RVSM equipped aircraft have priority, and ATC decides. If a non-RVSM will be in conflict with a RVSM aircraft the non-RVSM gets shifted. Every so often a non-RVSM aircraft that gets royally shafted bleats that he has to divert somewhere for fuel. Tough. Can't recall anybody being made unemployed or dying because of it.
The US, however, opted for an exclusive model for RVSM. Maybe somebody's agitation to standardise with US whims has resulted in the stated policy for ADS/B. The US has surveillance coverage across their country in Class A airspace. The proposed policy will deliver the same result here. Brilliant.
Maybe it is just the magnitude of the difference, which I'm sure some pilots wouldn't appreciate. Consider yourself departing YAYE in your RNP and ADS/B equipped jet, and there is another jet coming the other way under your intended cruise level. If you are both identified with ADS/B (and implementation has finished and we can use the radar standard) then the ATC has only to establish vertical separation above the other guy's level before you get within 5 NM of him, restrict you below until you have passed him, or vector you at least 5 NM left or right of him for an unrestricted climb.
If the other guy hasn't got the gear then you either get 1000' above him 10 minutes before the ATC thinks you will pass - could be more than 80 miles separation - or wait til you've passed (plus variegated procedural standards).