I see what you're getting at, lot of questions to be answered. Addressing the first one on your list, the whole game is set up on random and wandering spawn so and what your mentioning is no different from the garbage piles/ troll mounds that already spawn but they have to be destroyed before deeds can be thrown down and LOTS OF room on all the many servers we have.
Second, Lots of room on the servers , and the troll , crocodile mounds , and 'pile' spawners are still in place would still far outnumber what I'm thinking about.
Third, anyone who clears the area, yes I see where you could be going with this, maybe someone lures off the mobs while another whos waiting, hidden runs in and grabs the stash, could happen but , still more gameplay with it than without. I would like it to be after the mobs are cleared out, and they already have two mechanisms in place at Rifts and Slayings with submenus that look at %hits and number of hits and presences could base it off that, especially Rift scenarios.
Fourth, I haven't seen anyone wall off a Rift, however I have seen organized slayings that has been done at, but more-so to not let the unique leave the area or run away. I have seen walls at deed drops though(people protecting their share of the pie ( that could be addressed too if it gets answered with this. Also "tackle with a couple of their friends" is a great idea here, not necessarily meant to be soloed, could be an area effect like the Rifts, the more people the tougher and more mobs could be spawned, Now you gave me the idea of Micro-Rifts coming into to play leading up to the main Rift event. Scouter camps that tell of the "Great Rift" to come. (could denote where an eventual Rift may occur kinda like the Missions aspect of the game if not using that theme to deliver. "Rogue Rift/ Bandit/ Troll/ Enemy Camps have been spotted around F-H, 15-17. Just getting to energy here going...some system like that. Players will be players regardless of what you do to the game, programmers and GM's are always having to address PVP server bans and issues already anyway and players that abuse macros.
Now, good questions, my add was to toss new ideas out there, and enhance a venue of gameplay, not to say "Wurm is boring as it is, make me something new."(I love this game and where they have been taking it). But I am a person who dumps money in this game too, and it seems to me, I can post ideas freely here , with respect.