Not meant to be a slight, just adding another perspective for what is about to follow:
Leave them as they are. Here is why:
Currently, there are two kind of "extended" boss-encounters:
1. Claw of Jormag, several phases with an unique mechanism, no particular organization required, proper dps-phases helpful to speed up the already more than over-long encounter. All in all, boring and not very rewarding. But should it be more rewarding when half the people are semi-afk anyway and it can still successfully be completed?
2. Tequatl/Wurm, again the kind of unique mechanism you seem to be looking for, organization and/or even third-party applications (TS) required (especially in the later case). Unless you luck into an organized megaserver-instance, you will want to be on the map well ahead of time, say 30-60 minutes or whenever the crowd doing the organization starts gathering and this is basically what the problem boils down to: In my opinion, this game absolutely does NOT need more 30-60 minutes + event-duration encounters. I have no desire to spend one third to half my game-time of an average weekday on a single boss-encounter for a bunch of crappy blues, greens and rares.
So, to anyone who keeps crying about how Shatterer is boring and how every world boss should be like Tequatl I can only say this: Be happy while you can still hop on a random megaserver basically at event-time, get a few auto-attacks in and get at least the daily rare and some dragonite. This is casual, this is keeping the flow of the game up, this leaves you time to enjoy other encounters as well...
As a final note, I'm not against harder boss encounters as such, just don't put them in the open-world. Instead, do instances that can be triggered on demand. That way, all the ahead-of-event camping and organization can be greatly reduced.