1) You can theoretically win with 27% of the vote under the electoral college already
2) The two party system would still be a thing as long as first past the post is used.
3) I fail to see how it's a bad thing if third parties become relevant.
You're absolutely right. Two party system would be in tact. Think about it this way: we already elect all 50 state governors by a simple FPTP plurality vote. It would be exactly the same, but if the entire country was a state. Gubernatorial elections are almost exclusively two party affairs where the winner often has an overall majority.