Actually the progress IS saved after a boss gets downed. You merely inherit the raid leader's locks once you enter the dungeon. Lets say you don't have any locks and join a group for Turn 4. The moment you set foot into Turn 4 you inherit the locks from the raid leader (locks for turns 1-3 in this specific example). The lock for turn 4 itself will first be set AFTER killing the boss. This is the way any MMO out there handles it. And I already stated the reasoning behind this numerous times. The raid is build in a linear fashion, so you will have to down the turns in the given order. This implies that turns 1-3 have already been cleared (maybe not by you, but at least by the raid leader), there's no going back to clear them again, as being in Turn 4 means bosses 1-3 are already dead. It's like joining a party in progress in a regular dungeon. If you join the group for the last boss and don't beat it, you can't just warp back to the dungeon's entrance and all of a sudden the previous bosses are up and alive again. Locks save your progress and having a lock that grants access to a higher turn automatically implies that the group has already progressed past the previous turns. It works like this in any major MMO out there.
I'm all for your first bullet however. There should be a way to see which locks will be inherited BEFORE you enter the dungeon and you should not automatically be teleported into the dungeon once the Raid Leader steps in. The players should see some kind of confirmation dialog stating that they are about to join a raid that has already progressed beyond whatever locks the player may have themselves. Or if such a dialog won't be introduced, players should be provided with a tool so check which locks the raid leader has prior to entering the dungeon themselves (as locks are inherited the moment you enter the dungeon). By all means the players should be allowed to decide for themselves when they want to enter the dungeon. This forced teleport is just crap.
I guess the need is from people who either haven't played MMOs before or who don't get the concept behind raid locks and linear raid progression. I guess the confusion probably stems from the coil being split into separate turns rather then having all of them in the same instanced space (as most other MMOs out there do). If it was one space, people would physically have to walk through the areas that have already been cleared and see that no trash or bosses are alive in the previous turns. Having the coil split into five separate turns probably invokes the impression that those turns work independently, which simply is not the case.
No one loses out on their gear. You can't blame the game or the system if people are not able to down all of the turns within whatever timeframes they allocate for raiding. If a raid only invests 1 hour per week on raiding, this is hardly the game's fault. And to be honest, a raid that has all of the turns on farm can probably clear all five turns in less than 1 hour (I think there was already a thread on groups clearing the coil in such times). If someone loses out on gear from the later turns it's either because they just can't beat besaid turns or because they take a break after turn 3 and never come back during the lock cycle (which is entirely in their own responsibility). It's not like the game took something away from them or like the game locks them out from the loot. If people want the loot from turn 4 and 5, they just have to kill those turns. No rocket science involved.