Thanks for your question, AssetVotingAdvocacy. I like ‘tranche PR’! I am only just getting started with my local advocacy. As is of my nature, please let me bore you with a bit more useless detail.
Many of the things we call ‘systems’ are really comprised of a remarkably separated ‘frontend’ and a ‘backend’. Your radio has a ‘tuner’ frontend and an ‘audio’ backend. Voting systems do too. The key concept pertaining to the frontend is ‘expressiveness’, and the concept pertaining to the backend is ‘responsiveness’. Expressiveness is meaningless without responsiveness, and responsiveness is meaningless without expressiveness. If I gift you a lottery ticket you have vastly more expressiveness if I let you write in some number to be guessed. But still that ticket is of no more value to you if I insist on writing in that number myself. The random lottery system simply is not responsive to you in that regard.
Every election system has a frontend and a backend; these are the ‘balloting system’ and the ‘tabulation system’ respectively. Some example balloting systems are, score voting, ranked voting, approval voting, single-selection voting, and so forth. Suppose you have a ranked system ballot. The tabulation system (for the complete voting system) could be RCV/IRV. But the tabulation system could otherwise be ‘simple ranked voting’. With that, the first rank-place could be marked ‘10’, the next rank-place ‘9’, all the way down to ‘0’. With this type of tabulation you just add up the numbers that correlate with the candidates. It is just like score voting, but far less expressive, and so far less useful for the voters. Note: same frontend, different backend.
Now here is the really cool thing about (add-on) tranch PR: It will work just fine with just about any tabulation system! The balloting could be score, approval, single-selection, maybe even ranked for all I know. You can just add on the tranche PR backend and you are good to go! So now, you can righteously proclaim that any election system (including of course score) can easily become a proportional representation system. Cool!
My local election activism activity is only a few weeks old, and nobody’s mentioned the PR issue so far. We shall see…