There are a number of structural things you can do to push back on the long-run capture of parties and therefore the political process. None of them play super well with party-list proportional representation, but here's what people should be thinking about, especially in places with party primaries:

- Require party primaries to be as open and competitive as general elections. This is the traditional American approach, and for all of its own the failure modes that we've seen since 2013, you can't say that the problem has been beigeness enforced by party elites. Ask Eric Cantor, Jeb Bush, and Joe Crowley about that.

- Replace party primaries for single-member districts altogether, with open primaries with STV or approval voting. That gives even more room for policy entrepreneurs whose appeal may cut across existing party power bases.

- Make heavier use of Sortition and/or policy juries, delegating decisions to randomly-selected deliberative bodies. That gives you lots of democratic legitimacy in a way that's very hard to capture. Tellingly, this approach is already used for the State's most dangerous powers around criminal punishment.