I think it's a fair trade. Unlike the County Championship where the bulk of the manna falls from heaven (i.e. the ECB) the Test cricket world is all subsidised by the revenue from the Australia-England, Australia-India and England-India series. Not one other Test series manages to pay the bills these days.
It's in the interests of the other seven full members to allow the subsidy from the big three to continue - and giving a little special treatment to allow that to continue is a fair trade. With the exception of maybe the South African board, they all know which side their bread's buttered and will pass the vote comfortably knowing that the alternative (total deregulation of Tests and even less subsidy from the big three) is far worse. South Africa might oppose it in debate, but they need the cash from the big three too much to vote against.
Australia may have been ranked #5 until recently, but it's a long gap from there to #6 and I don't think we would have lost a relegation playoff to Pakistan even at the worst of our 2009-2012 form slump. I do think it would be more interesting if it were six teams in each division, with Ireland and Afghanistan promoted from first class to Test division 2.
I don't think the proposal outlaws inter-division play though, we could still see things like England having a couple of matches in Sri Lanka as a warmup for India, or Australia hosting 2-3 short series against second-tier opponents in the summer leading up to a World Cup.