Totally agree with you... kinda. The idea of the Rolling Mists myth has been one that I have supported for some time now. I think that this idea of the Mist moving ahead and revealing new items is possibly true... however, that would negate the idea of The End of the Way. After all, if the Mist is always moving forward, the Way ends in a different spot every second, yes?
But it would certainly explain Gaius's claim that the cave used to be the end of the way, a claim you could make of any given spot on the way. Keep in mind that Gaius is the only one that ever names that area as the end of the way, it would be absurd to actually consider it such, seeing how close it is to Estrana, a place that must be many decades old.
I do not, however, think that there is Mist coming from behind, swallowing poor unfortunate stragglers. My evidence? Estrana. The fact that a settlement that large could stand for hundreds of years without being engulfed by the Back Mist seems a little fishy. Certainly, if such a Mist existed, it would have covered the city by now.
Well, the way has to be
really big. And the portion not covered by the mists(if they exist) itself must be big enough that the area where the game takes place is at least a good hundred years ahead of the mists. This is because like was said, not only does it take a long time for a city like Estrana to be built, no ones even going to bother if they think the mists are coming any time soon. So the existence of Estrana doesn't disprove the mists, but tells us more about the world (or at least the peoples perception of it).
As for the Way being a Loop, you might have several things to back up your theory there. For example, Rhue (or Jeruh, or whoever) leaves the Landorin Stretch as a child, and continues walking in a particular direction. However, by the end of Episode 5, he's right back where he started? Why? Maybe because the Way, being a loop, forced him to go full-circle both physically and metaphorically.
The way being a loop is all but a given at this point, because of the evidence you give, but you got it mixed up a little bit. The place Rhue arrives at at the end of EP5 is not Landorin, its the place that was Landorin in Rhue's mind. We see what the real Landorin looked like at the end of EP6. This means that the place Rhue thought was Landorin is from a different memory in his mind, and somehow got mixed with the Landorin one. (Re watch the conversation with Gaius at EP5 now and a few things Gaius says will make a lot more sense now). So Rhue has been there before, but we have no idea when. Given the supposed size of the way, it must have been a long time ago, which adds to the claims that Rhue has been around for a long time. The Way is certainly not a place that can be circled in a decade, if it was, people would certainly have noticed.
Also, to go back on a previous thing you mentioned. You say you believe that the way loops, and you believe their could be mists at the front of the way, but you don't believe there are mists at the back of the way. If the way is looped, and there are mists at the front, then there
have to be mists at the back, because they would be the same mist, it would just depend on what side you are on.