Being a republic is completely orthogonal to whether elections use 'winner take all' or 'proportional representation.' Third parties may not be viable in a winner-take-all system, but they work just fine in a proportional representation system. The suggestion is quite workable, the only issue is whether it can gain enough popular support to be implemented.
Ummm.... yeah, "orthogonal"... what he said.
A far more linguistically-economic statement of the case than my #21.
But, same point... ;-)
We weren't set up to havce what you imagine it is that you desire . That too, makes it a moot point. OTOH, should ( GOD forbid ! ) you get what you claim to want, things would be untenable . Why ? Because the lefties would have more power than they do now, Conservatives ( and some socalled Conservatives ) would do what they ALWAYS do ; bicker / fight / get nothing done, and hand it all, on a silver platter, to the Dems/ Liberals / faaaaaaaaaar lefties. Doubt me ? Don't ! Look at the way the GOPers and the fringers fight on FR.