"Rank voting" is dozens of different voting systems; its essentially one of the major kinds of ballots -- FPTP-style vote-for-one ballots are used in two main voting systems (both often referred to as FPTP): plurality and majority-runoff; "rank voting" is used in many voting systems (IRV, Borda, Bucklin, Coombs, and pretty all the Condorcet methods); and there are a few voting systems (e.g., approval) that use different balloting mechanisms -- though most of them (including the FPTP style and the approval style ballots) are special constrained cases of rank voting ballots.
> In short, the voting system is ingrained into the constitution and will not change in the foreseeable future.
Actually, nothing in the Constitution requires either FPTP or single-winner constituencies (except, arguably, indirectly single-winner for Senate seats by way of the 1/3-per-two-years requirement.) Forms of FPTP -- both majority-runoff and plurality -- are adopted as matters of state election law, and single-member, geographically-defined legislative districts have been required since the civil rights era as a matter of federal statute as a response to states that used FPTP in multimember state-wide districts to effectively disenfranchise minorities (the same could be prevented while allowing multimember districts by using a system that produces proportional results -- including candidate-centered systems like STV as well as things like party-list proportional.)
Very little of the US system of elections is set in the federal Constitution -- about the only part that is is the Electoral College for Presidential elections, and even there the matter of how electors are chosen is expressly left to the state legislatures.