The thing about lore is it is always constantly evolving. There is no telling what will happen in 5 years and how the current lore will evolve during that time.
I don't think VR has said anything about lore being "locked-in". However, I think they have a plan for the story they want to tell and are working on implementing it in a way that makes sense. It's hard to know where the story will go after the game launches and what might be expanded upon, or clarified. However, I don't think that the team or their lead writer would implement something that completely throws out decades of lore, just so they can implement something that makes sense.
It is a bad comparison for VR since it will of course be new writers coming in who have not even read the lore, but of course have a vision. (Sheds a tear for star trek) I am more curious how far is planned out lore wise. They talk about planning the game up to lvl 100. Is the outline for the lore planned for that as well or only stats up to 100?
I ask in part because there is a lot of benefit from planning some of the things like new classes. For instance if they plan to have a beast master class in about 2 years post launch, VR can create limited beast master NPCs into the game we simply see around. Perhaps out on patrol or defending wilderness settlements. Even NPCs we are killing like goblins could have tamed wolves, etc. People would see it there and know it is coming some day. Same with anything else like if they wanted to build a 4th nature themed tank or an arcane healer. Having them in the world but being very rare foreshadows their introduction in a pleasing way.
I am all for any hints and suggestions being introduced in game play, whether that is a new class or lore or event or anything.
Say if a new zone is going to open, then around its edges and bleeding into adjacent live zones, we could have animals, mobs and npcs wandering around. Perception pings could be utilised too. Yup I am all for adding suggestions ingame upcomming expansion clues and the like.