The issue King has raised was in fact brought up, debated, and settled at the time the bill was passed. It was decided that the bill did not contradict the constitution in any way, and therefore did not need to be an amendment.
It was not discussed in the original thread where the Preferential Voting Bill was debated and voted on. The only discussion was when NickG asked if it was an amendment or a bill and StevenNick said a bill. No Senator officially questioned whether it was vaild or not...
The Constitution does not specify the method of counting votes in Senatorial races whether it be first past the post, approval or IRV.
Article II Section 2 Clause 5 might cause problems for the validity of Presidential elections held since we went to IRV for Federal elections so that any of the slates that were listed on the ballot last October might be able to sue, depending on how that clause is interpreted. If it is interpretted as a ban on runoffs in Presidential elections, then the Senate should be electing the President as no slate got a majority of first preferences.
We may indeed have overlooked that clause when we (correctly, otherwise) determined that IRV was not unconstitutional. Or maybe we interpreted it to suit our will, I don't know.
Do you think it's worth a try? Everything to get the current occupant out of the Veep's mansion!
No, seriously, I don't.