So far details on Rise of the Rajas is sparse but we do know that it will feature performance updates as well as some major balance fixes.
"This awesome expansion is set in southeast Asia, and brings tons of new content as well as some serious upgrades to the quality of life for our Age of Empires II HD. We’ve had an open beta over the past few months to identify and correct a few performance issues, and with your help we’ve managed to reduce desyncs by 90%! With today’s announcement of Rise of the Rajas, we’re also pushing these performance upgrades live to all of our players for free. Among other things, this makes multiplayer matches much more stable, AND we’ve added multiplayer restore back in, so if you ever DO lose a match in progress to a desync, you can get it back and pick up where you left off!"