Just an update on what I found after going through PVG:
1) YES, DL can interline and check the baggage all the way through final destination. (Now getting your baggage in your final destination is a different story. We 'lost" one of our bags. It took a week and in a different airport before I got the "lost" bag. Long story that will be covered later.)
2) DL couldn't issue my boarding pass for the MU leg. However, online check-in is possible with MU and I was able to print my boarding pass. Interestingly, MU was able to print my boarding pass for my DL legs on the return flights.
3) There is a transit desk in PVG that issues boarding pass.
4) I-I transit at PVG is easy, simple and quick. Signs are everywhere and the lines were short. Fingerprint for all non-Chinese passport holders is required though even on I-I transit. It is all automated and very quick, so it's not a big deal. Also, you get a receipt that you had your fingerprint taken by the machine, which can be used the next time, which I just showed the receipt on my return flight. Overall, it took me about 20 min after exiting the plane, walk to fingerprint area, get fingerprint, walk to transit desk (which also has automated area if you already have your boarding passes), walk up to security and into international gates.
5) I didn't need to get my luggage and go through custom for I-I transit as they were checked in all the way to final destination.
6) Skyteam lounge at PVG is nice with showers. Downstairs has all the hot foods including a noodle station and all the seating area has tables which is set for eating meals. Upstairs is more quiet, seating is more like standard lounges, with some recliners and massage chairs and only has drinks and small sandwiches and cakes. There are showers on both floors. Sign up at the counter. Showers are nice and well equipped with toiletries, hair dryer, etc.
7) Security line is very strict with lithium batteries. Power banks will be inspected and need to be out together with all electronic devices. There's a limit of 100 Wh.
8) Baggage security is very strict. One of my bags that was delayed was held by PVG security because it appeared to contain a questionable item. Questionable item was a new watch still in it's box. It was a gift for my sister. Maybe they thought it was a bomb with a timer. To add to my bad luck, the bag was "locked" with one of those built in the bag combination zipper lock. The combination was 0 0 0 and it was set to it and i just just "locked" it to prevent the zipper from dangling and breaking. I had to sign paperwork authorizing them to open and "seize" the security item. They actually didn't take the watch after they opened it. I did get my bag but I was already at a different destination (Taipei). CEB couldn't locate the bag but China Airlines staff at Taipei (they take care of lost/delayed baggage for Skyteam at Taipei) found it, told me the problem and got to me the following day but that was already Day 7 of my trip.
9) I only heard this from the FA on the DL flight but she told me that Chinese military will stop all commercial flights flying out of PVG indiscriminately throughout the day, but mostly at nights, which will lead to flight delays. And this did happened to my outgoing flight to CEB, where we were delayed for almost two hours. Because of this delay happening a lot of times, my return flight from CEB to PVG was delayed also. Note that my flight back to the US and all other international flights that morning were all on time. So make sure you have a long layover in PVG for outgoing flights back to the US.
If you have questions about transiting via PVG or connecting with MU, I would be happy to answer what I know from this experience. DL FA told me that DL is trying to see if MU and PVG can be a good gateway for DL to Asia as NRT/HND is out of the question for DL since Tokyo is not being very helpful to giving them more access. PVG is currently building more gates for its Terminal 1. So PVG might be the main gateway to Asia for SkyTeam.