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You specifically noted Europe's "highly interesting mix of concurrently running competitions" as the reason fans are so engaged.
I'm merely observing that all the empirical evidence from this neck of the woods is that the majority of Australian supporters struggle to follow both SR and club rugby at the same time, or the NRC and Wallabies in overlapping windows, and can't even manage consecutive competitions like the NRC following on after the conclusion of club/SR. Never mind the mental implosion and widespread supporter disengagement once SR was any more complex that a simple round-robin.
You say interesting, and I'd agree. But all the evidence is that if they had anything like that here, the bulk of supporters would actually see it as baffling and probably distressing. They've struggled with the most basic of changes as the professional environment has evolved; that sort of complexity would probably cause mental health issues.