Sure we can make a UO client and a UO server that emulates the original perfectly, but UO didn't exist in a vacuum. Unless it's 2001 and UO is the only (mostly) large scale MMO in the market it's simply impossible to recreate the experience. The variety of playstyles that were forced to coexist in MMO haven't been seen since and probably won't be seen again now that it's not the only game in town anymore.
One could say that the world players wouldn't have it is the same, perimeter-wise rule-wise. But the people how the interacted what the Norms were and all of that other social human stuff is what we can't go back to.
And all that is a huge part of the game value for people, the Memories they have the feelings surrounding all of it.
