Outage due to Replica Set Protocol Version upgrade?
What that protocol change do, is change decision pattern what nodes do when new primary must be elected. At the situation where all SECONDARY nodes are up-to-date (not falling behind) and your current PRIMARY have higher priority than any of SECONDARY node, nothing will happen. The system continues as it was.

But afterward, if your current PRIMARY is unavailable, next primary is elected faster than it was with protocolVersion:0