Go-Go Instant Runoff Voting! ... The only people I can imagine being against it are the most cynical of the entrenched power elite. I think we'll all be doing IRV eventually.
I doubt we ever will, and for precisely the counter-reason you suggest: that it would endanger the dominant parties. The people will never be able to accomplish anything that endangers the political status quo so fundamentally. To be more blunt, one of these two political behemoths (the one that rhymes with Shmepublican) is tremendously good at taking any benign issue and turning it into a terrible communist plot. Examples:
- Campaign finance reform. Large companies that stand to benefit much from inclusion in federal budgets bribe our politicians and then wait for their kickbacks. Conservatives hate government spending, but don't seem to mind the bribes that lead to this spending.
- Health Care. I live in Massachusetts and am very familiar with which party invented health insurance mandates and state insurance markets (hint: our governor at the time has also appeared on Sesame Street as a game show host).
Instant Runoff Voting is a great idea, and one entirely compatible with conservative ideas, but that doesn't matter. If it were somehow to gain a public spotlight, the Republicans would do the same sort of thing they've done to other good ideas. IRV would become Tea Party fodder; they'd ignore all specifics and call it Instant Rigged Voting. And the media, which also ignores all specifics and strives to cover controversy, would fuel it. Sorry if I'm a cynic, but I live in the United States and have been paying attention for the past decade. The country's ability to communicate effectively and think independently is broken, and we won't have things like IRV until or unless this changes.