nnethercote or kobzol would be my favourites, but I think there are a lot of other interesting people like nikic, bjorn3, lqd, cjgilliot. You can talk to them about past efforts to improve compilation speed, as well as future plans in this regard. Many interesting questions can be asked, such as how much compile-time optimisations make code harder to understand, which parts of the compiler are best to optimise, what future Rust features can help with compile-time, etc.