It's called a contest, but to be honest, I consider it a lost chance.
Even what the UO dev team once designed, is just one big horrible chunk, most probably, based on the motte & bailey fortress in Roman style with a central donjon. To be more precise, based on the uninhabited ruins of a motte & bailey. And simplified, of course, so that it could fit on a castle-size plot.
Castles are so much more than this. They weren't just inhabited by one person, but a by multitude of people who had different professions, and therefore different houses.
Also, they come in plenty of styles: Gothic, Renaissance, Baroque, Rococo, Romantic, Classicist... They were meant as a place where people could protect themselves, hence the many towers which later evolved into status symbols.
The Loire region in France alone offers nearly a hundred castles, each one completely different. And that's just one region in one country. There are 50 countries in Europe, and Europe is only one of the continents on our world where you can find real castles.
Borg cubes are fine... they're great... for a nice sci-fi dystopia game where such a construction would make sense. If it's true that UO explicitly said "no cubes", then why can we vote for them? I expect they didn't really mean it when they said they'd disqualify them. It's a terrible shame. I read about functionality in this thread, but what does functionality have to do with an MMORPG game? Leave functionality to bookkeepers and industrialists. Weren't we playing UO for the immersive experience once?
Many people just threw something together in half an hour, not even bothering to put a roof on their walls. If you want to do something truly well, you have to be prepared to invest time and work in it. Rome wasn't built in a day either.
I've seen only a few designs that are based on real (still inhabited) castles, and / or where a decent amount of time and effort was involved. Those are my favorites. I applaud the creative minds behind these.
More rounds are coming, and I hope those few master builders will continue to design castles and keeps that resemble our RL heritage more. It's a pleasure to visit them, and I could live in any of these.