Spent 2 years soloing a deed on a warfront, a true citadel given a good population would appear. 5 tiers of perfection with over 100 buildings, an elevator, quick release mob pens, traps and other unique quirky features found no-where else then one time I was late with upkeep and it disbanded. No middle ground, just all that effort gone in one tick. Still gets to me now and I haven't played since but unless you automate things or put a ton of upkeep on the same will happen to all of 'em. I particularly would love an exact template of mine at it's peak that I could load in to WU or similar.
Offdeed decay. Scavenging abandoned places used to be one of the joys of Wurm, possibly my favorite one. Many a gaming forum collective have passed through the servers leaving cities of decaying fun to rifle through. A small amount of decay is a wanted feature I expect but the levels I remember were pointless and killed most of the exploration for me.
I also think it would be savvy to let f2p ride horses. I mean just about, with 19.9 BC so they could be top of the f2p pile and give the f2p players it's own culture. Much player retention has been missed there for sure. They may be shanty towns but so many would prem that Wurm wouldn't have a problem any more. I think riding would do it.