I would throw Darkfall into that mix. I agree with some of your points, and think that EVE Online can't be ignored - it has some of the best PvP around as far as consequences and the like, and it's a sandbox, but you are leaving out two very important things.
EVE Online doesn't have a lot of competition. Many companies aren't going to risk that kind of hardcore PvP where you can lose everything, and having a single universe (two if you count the Chinese one) is also something that companies are wanting to avoid
The second is that around the time UO started declining after 250,000 subs, that just so happened to be the true rise of MMOs. EverQuest, Camelot, AC, those were the biggies for UO's early years but UO was still the "first" and still had a lot of momentum or it would never have gotten to 250,000 subs, but around the time leading up to AOS and the year or so after, you started seeing EVE Online, Star Wars Galaxies, and the elephant in the living room, World of Warcraft, which was coming out of beta and had the media's attention, plus EverQuest II and some of the others. Things just exploded after that, especially in Asia. There were so many choices, and some of these MMOs had built-in fanbases such as the Warcraft franchise.
A third could be UO has also gotten hurt by major layoffs or reassignments, and with all of that, there wasn't a guiding vision that everybody stuck to. One year they were moving towards a 3D game, the next that was put on the back burner, the next they are moving towards a Diablo-like game as far as items, etc. UO bounced around way too much and it still does in 2011, and because of how it started, it never had a solid gameplan or was as carefully guided as say EVE.
With that said, had AOS not happened, I think UO would have still lost subscribers. Too much going on in 2003-2005. I think the amount of subscribers it's lost since 2004 is alarming, but that's not say to that it can't be reversed with solid support from EA.
I hate to admit it, but I see the point of the classic sharders. I don't think it should be a priority, but I am coming around to them doing a classic shard, maybe as a 15th anniversary. I don't think a classic shard is for me, and I wouldn't play it, and I think many wouldn't leave to play it, but I'm seeing the appeal.
So mark that on your calendars, I have admitted that a classic shard is not a bad idea. I just think it needs to be further down the list of priorities.