Mixed member proportional representation (MMP) now seems secure as our electoral system. No parties or pressure groups are campaigning for a return to the past.
Yet MMP is under threat, and Maori electorates are partly to blame. The threat arises, however, from electoral mathematics, not today's politics.
Don Brash's controversial suggestion that Maori electorates be abolished has not yet formed a part of today's debate about Maori indigenous rights. Rather, today's biggest electoral issue is the prospect of an electable Maori party winning those seats.
Labour's Maori caucus may defect over the foreshore and seabed issue, it is suggested, thereby creating such a party.
Our version of MMP is set to disappear in a few decades as a result of the special provisions it grants to Maori and to South Islanders. The legislation upholds a fixed South Island quota of 16 electorates, and an expanding quota (currently seven) of Maori seats.
Ever since the South Island quota was introduced in the late 1960s, it has had the effect of steadily raising the number of electorates in our Parliament. This is because the population of the North Island has been growing faster than that of the South.
Conservative projections suggest that list MPs will be entirely eliminated by the 2041 election. The historical rate of growth of general seats has been 1 per cent a year. If anything, with both international and domestic migration favouring the North Island, the rate in which new general electorates are created will accelerate. At 1 per cent annual growth, we can expect to have 74 general seats in 2020, and 90 by 2041.
The growth of Maori seats is harder to estimate. More because of genetic drift than because of higher birth-rates, the proportion of New Zealanders with some Maori ancestry is likely to increase by at least 50 per cent per generation throughout the 21st century.
The number of Maori seats grows also as Maori become increasingly aware that voting on the Maori role is no longer a wasted vote. My estimate is that there will be 16 Maori seats in 2020, 30 in 2041.
If I am right, there will only be 30 list MPs elected in 2020, one-quarter of the total Parliament. Mathematical analysis suggests MMP breaks down when less than a third of MPs are list MPs.
If the Electoral Act is not changed, overhang (that is, extra) MPs will become the norm from the 2010s. In the process, we can expect a senior list MP such as Michael Cullen or Dr Brash to become a victim of this numbers game.
Indeed, in 2005, a surge in support for National electorate candidates could put Dr Brash out of a job. (Watch out for a "one-tick" National campaign next year).
From 2014, probably all list MPs will be opposition or minor-party MPs. This is because the remorseless logic of voting at the electorate level gives a significant excess of electorate seats to the least unpopular party, even when that party gains well under 50 per cent of the total vote.
What can we do to delay or prevent an ignominious death-by-inertia for MMP?
We could discourage Maori from joining the Maori roll. Or we could subsidise emigration to the South Island.
Legislation to abolish the South Island or Maori quotas would meet stiff political resistance. A referendum to abolish either quota would probably succeed, but at the cost of exacerbating existing social rifts.
There is another scenario that requires no political intervention but could be seen as a gerrymander to keep the Government in power.
Labour's compromised Maori electorate MPs could stand as Independent Labour at the 2005 election. Labour, seeing an obvious silver lining from this dark political cloud, would not stand candidates against the Maori MPs. Most Maori voters would cast their party votes for Labour, while voting for the re-election of their existing electorate MPs.
The result would be seven overhang MPs, all pledged to support Helen Clark's Government on confidence and supply. The Maori MPs would be additional to the usual 120.
In the wake of such a result, the Clark Government might be tempted to legislate, to make Maori seats permanently apart from the proportionately elected 120. This could be the beginning not of a Maori Party but of a Maori Parliament (or Senate).
The same overhang scenario unfolds if the present Maori electorate MPs form a new party. While winning all of the Maori electorates, a Maori party could be expected to win little more than 1 per cent of the nationwide party vote. Maori would exert disproportionate political influence through their overhang MPs.
We have a situation now that, if not addressed, will lead to substantial constitutional change through MMP's unlocked back door.
The removal of the Maori seats from the proportional equation (or their removal altogether) would not be a permanent solution to the progressive degradation of MMP. Either the 120-MP limit or the South Island quota will have to be abandoned.
* Keith Rankin teaches economics and statistics at Unitec.