I would like to see combat dummies, either placed by players, set up as world projects or just placed by the developers.
I picture these dummies to have, say a finite amount of hitpoints. Perhaps different types...
I could build two of them on my plot, and stage contests with other players - the winner being the one destroying the dummy first of course. As all hitpoints depletes (perhaps in stages too), the dummy will fall apart and take a few minutes until it respawn again.
This could be fun to watch for a crowd as well. And people can showoff combat-moves and spells if they like. It will create a new area for roleplaying and people to come together. As it is now, people rarely stop to look at and enjoy the built areas, mainly because there is no reason to. Crafting 237489 iron bars is done by a few clicks, put them in a silo, process again, in to vault... you get the idea. Plots are often abandoned, but structures like this can perhaps make it worthwhile to go there to share som fun with others. Harvesting takes time, but that is rarely a place where you're able to interact much either.
I suppose it is not too hard to design the "combat-script" on this dummy to /say damage taken, time elapsed, name of the winner...
Different tiers can exist too. with damage threshold for instance. Can be used to prove ones prowess for instance. "When youcan slice the head off of the dummy in onechop...you'll be a full member of the guild..."
You can have player held archery contests.