This was under consideration at one time by the Seattle build team and was a recurring point of discussion during infra summits. Unclear if we actually broke ground.
Just saw your other comment. Not sure exactly when you left in 2018, but around that time, there was an internal summit involving various platform/infra orgs that decided to invest in Bazel as a company-wide standard. Java is still on Buck due to some technical reasons, but several orgs are either moving towards or already fully on Bazel.