Yeah, the gates are possible problems in many other dungeons too. 69 and 79 have bh bosses as gatekeepers, for example. I wonder if there is a way to just remove the gates and not the mobs/bosses linked to it, maybe?
Assuming we are treating the shared instance separated from the regular one, and this exclusive/regular option would remain as it is, the camping bosses problem would be a thing only in the shared instance because of the boss respawn time, right? In that case, if we increase the boss respawn time from the original 15min to 1h, would it be too bad? It's not like the shared dungeon could be "reseted" like the exclusive ones, so the respawn time would affect other possible groups that decide to go for it in a different time... My concern is that different groups would be limited on their options to start a shared instance by another group that started it earlier and be "forced" to get an exclusive dungeon to do the bh or wait for the respawn (not sure if it's bad too...). I'm really not sure how to address it, I particularly liked the option with 15min respawn, but I feel like it would be exploited to farm specific drops from bosses, on the other hand, a higher respawn time would affect other groups (although it's not like we have that many squads going for the same dungeon atm...). Maybe gather the options and do a poll on it?
About the log in/log off mechanic to be booted after 4h in a dungeon, I didn't know it existed here, since there is no msg when you enter the dungeon... but I never tested it.
About the loot sharing, if the most interesting loot is tied to the quest at the entrance and if the kill count could be obtained by everyone in range of the boss, I think that would be solved, I agree with Beta that the regular drops going to the squad/player who killed it is ok (considering that would not be the most interesting reward). But I'm not sure it works that way, I believe you don't get the kill credit/count by only being in range atm, you need to be in the squad with most damage or you don't get the credit. I didn't test it, but that is something we should verify and confirm if the kill credit based on "just being around the boss" is doable.
The shared instance would introduce some new forms of pvp too (inside dungeons...), for whoever is in white name. It would be interesting to see how it would go xD