There's obviously nothing explicitly preventing Blizzard from doing such a thing, but I do see two major problems with adding Lorewalkers as a specialization for bards.
First, Lorewalkers seem to be pretty heavily established as non-combatants. Lorewalker Cho, the most prominent Lorewalker, doesn't aid us in combat whatsoever, despite being present in a bunch of raids and quests. It's entirely possible to change their image by focusing on their desire to explore and unearth secrets, but that simultaneously ruins part of their original appeal as a group and distances them from the aspects that make them fit with the bard class.
My other point kind of stems from this. What makes bard the most suitable class for a Lorewalker spec? Personally, I think they'd fit much better in an explorer-type class. As it stands now, the elements of Lorewalkers that would be more likely to fit in any given storyline and give them more of a reason to engage in dangerous situations, are ones that would also make them gravitate towards the explorers in the Explorer's League and Reliquary. As a bonus, explorers are pretty much a staple of WoW's identity at this point, whereas bards would just dilute it.
That said, I'm not super keen on a playable Lorewalker spec or an explorer class, but they do seem like better options. Bonus points if it encourages Blizzard to do something with archaeology, even if it is just giving it a merciful death.