The current boss of China Eastern is the former boss of China Southern, who brought China Southern into Skyteam. I guess he was too lazy to look for new connections, so he did the same for China Eastern.
You can earn and redeem Delta Skymiles on China Eastern long time ago, but Delta charges fuel for redemption on China Eastern.
China Eastern has the oldest fleet among all Chinese airlines, they still have Airbus 300 currently in service. None of their Aircraft have personal AVOD system in economy.
The good thing is, they do have pretty good award spaces on transpacfic route.
Don’t know whether Delta will give Elite bonus on MU flight or not. and one more thing, If you are Delta Skyteam Elite Plus, you can not access to China Southern lounge for China domestic flight unless you have international connections within 6 hours, so I guess MU will probably do the same once they join.