I doubt he’ll support PR. The Liberal Party benefits from FPTP more than any other party. They stand the most to lose from a PR system.
There’s no good reason for PR or nothing. RCV or even top 2 runoff (not as good as RCV, imo) can be legitimately preferred.
See: A Simple Guide to Electoral Systems. It’s still a work in progress, but lays out a good framework for discussing electoral systems.
We need to stop seeing PR as anything except citizen’s having the most to gain under PR.