One of the criticisms of MMP is that it allows politicians voted out by their electorate to get into Parliament on the party list. I haven’t actually seen any evidence that the public considers this a problem, just endless claims to that effect made by political elites. Consider the recent by-election in Te Tai Tokerau. Did the electorate ‘kick out’ Kelvin Davis? Are they outraged that he’s still in Parliament because of the list system? Of course not – on the contrary, they voted strategically so they could have both Davis and Hone Harawira representing them.
So how’s this as a compromise measure, an amendment to the current system if the nation votes to retain MMP in the electoral referendum: if a politician loses an electorate by a significant margin – 25%, say, then they can reasonably said to have been rejected by the voters, and they’ll be struck from the party list for purposes of that electoral cycle. This addresses the ‘kicked out and snuck back in’ complaint – if voters really want to kick someone out they can.
Update: incredibly obvious flaw, pointed out in the first comment: this would stop minor parties from standing in electorate seats. Slightly more complicated solution: you get struck off if you get >25% less than your party’s nation-wide vote?