This makes me even happier that LotR has them appendices.
BUT, those appendices are icing on the cake and would be a nice bonus after adding some actual meat to the endings. There was also 5 chapters of resolution, and Scouring of the Shire would probably be a DLC these days.
Harry Potter isn't nearly as detailed in the ending. After all, why include a bunch of details when you can leave plenty of room, since it's a veritable gold mine for future content. In spite of that, it provides enough closure to go on with. The only thing I wanted to see was Harry talk to Snape's headmaster portrait. He'd probably still give him crap but maybe a wink as well.
My brief outline for a possible ending fix I'll reiterate here as quickly as possible. Shepard defeats Reapers, but isn't the same. Be it PTSD or lasting indoctrination, Shepard is a potential threat. Choose life, death, exile. Before that choice, reunion with crew, learn of their future, maybe have some influence, possibly take part. Can't break up with LI at this point, but can choose varying future, within and in addition to life/exile.
Adopt a Krogan! Go deal with a Yahg threat. The galaxy is still filled with criminals and mad scientists, i.e., Omega and Henry Lawson's twin brother!.
If I want more ME3 content, aside from fixed endings (assumption atm, of course), I want stuff I care about, getting back to OP theme. I'm not going to care if everything still results in the current endings. Period. They are unredeemable if left in this incomplete state. You can add a new character here or there, a LotSB type of mission.
ExoGeni and Zhu's Hope could provide some albeit cheesy, "The Thorian was merely a setback..." DLC but you get the idea. Sha'ira the Consort, Javik, a rogue spectre, A volus/Elcor/Hanar/Drell plot. Turians gone wild. Yahgtzee mini-game!