I understand your intention but to be honest I don't like this idea.
Camping is boring enough but to run around hours on end would be even more boring and higher levels would most likely still be able to monopolize these bosses due to haste boots/carpets/sleds/brooms.
Back when I used to play ultima online a lot of the bosses/rare spawns on our independent server used to be like that and I can tell you out of experience that it was incredibly boring to be constantly on the hunt and usually just a waste of time. (granted the uo world was much bigger than Lirs Reach but I used to play on a pvp server so there was at least always the thrill of running into "player killers")
If you seriously hate camping monopolizing clans, this is the solution. You can't argue against it because even with +1000 speed, lirs is big enough so that they can't find it instantly like they did with Ythair.
Ideas perfect in my idea. The boss could have no aggro range for all I care, he should walk the entire lirs reah area.
Sorry, but take the midsummer bosses e.g., your proposal would have somehow worked for Sunclaw maybe even hatchlings but you still needed a strong group of 100+ for solstice drakes and an even stronger group for Ythair. So in the end nothing would really change we would just have to do a lot more travelling, personally I don't see the benefit.
BTW in my experience most higher levels (myself included) eventually grew tired of Sunclaw, hatchlings after a short while and gave a lot of those drops away for free or didn't even show up at their spawns. Ythair is certainly a different story but he's an end game boss (sort of) and there are still not that many who can take him.
And given the choice between camping for a couple minutes and hunting for an indefinite time span, I definitely prefer camping at least I can chat with someone while doing that...
+1 for some sort of kill range for bosses. If you are level 145 you would not be able to fight a level 80 boss.
A kill range for bosses is the worst idea I can think of given all the quest items you need. It took me way over lvl 90 to get all the space rems I needed e.g. but following your proposal I shouldn't be able to participate in a Rockbelly fight at lvl 120??