MDEV-29668, SUPER privilege won't allow many activities that it was allowing before.
Upgrades are handled by the server, a user having SUPER will have all necessary privileges after upgrade to 11.0 to continue doing what he was able to do before.
But replication isn't, if someone is granted SUPER, he'll be able to do much more on the 10.x master than on the 11.0 slave. This could potentially break replication if that user will do something that he can on the master, but not on the slave, and this statement is replicated. For example, CREATE DEFINER=xxx VIEW.