Long - so TL : DR - Forget about the "leaks" and speculation of naga/void/old gods (or any other themes) for a minute and lets talk about what features, improvements, characters, etc. you want to see in the next expansion.
I don't know about all of you, but this is my favorite time in the WoW cycle. The story of the current expansion is coming to a close and the eyes of the community are turning ahead to what comes next. The wild speculation - often horrible, but sometimes so close it becomes a true question if the "leaker" was leaking or just got lucky - always gets my hype meter rolling just a bit. Often, however, the hype for me isn't so much about what the new expansion will bring, but to see what amazingly creative (and sometimes not so much) ideas that the WoW community has.
As I have read these recent speculation and "leak" threads popping up here, reddit, wow's forums, and other sites, I noticed that this time, many of the "leaks" often have a drastic number of similarities. In this case, I think a lot of that is because Blizzard has done well in Legion with planting possible plot seeds that could develop down the line, but I have to wonder if this is constraining what these speculation and leak threads are all about - What does the WoW community want from their next Expansion?
Members of the community have become very hung up (and likely they are right to do so considering those "seeds" Blizzard planted) on a few basic themes for the next expansion - Nautical, Naga, Old Gods, Void, Island Zones, etc. The point is, that almost every recent "leak" covers these exact same tracks - which means that the big question, "What does the community want to see in their next expansion" is likely being forced to fit a speculative mold of a Nautical, Naga, Old God themed expansion - and that just muddles up the entire point of this part of the WoW expansion cycle.
That brings me to this thread, and my question. Take a moment and forget about Naga, Old Gods, and the other plot seeds that blizzard has planted and instead ask yourself these questions - What do you want from the next WoW Expansion? What features do you want to see stay or go? What places do you want to see? What characters do you want to see developed? What races and classes do you want to see?
For me, I really want to see some of the other leaders come into the forefront of the story, like Baine getting some development outside of books, or some movement with the Gnomes - perhaps it's time to finally give up Gnomergon and start anew.
I would like to see the idea of post max level character progression further developed - perhaps adding in a bit more customization in the choices we make. Instead of having a set group of class or spec specific bonuses, maybe we go broader and allow us to follow the teachings of a Titan to improve what we wish (Path of Titans revisited perhaps?) Maybe a player that would like some crafting bonuses would choose to follow Khaz'goroth for bonuses to crafting and mining. Maybe this same path can also offer bonuses to health and armor, or fire and shadow protection and damage. So, an arms warrior that follows Khaz'goroth may get a fire dot attached to some of their abilities, or a fire mage may just get some bonuses to their damage. Perhaps following Aman'thul gives you a self rez that you can use every few hours - even in a raid, or Golganneth grants you permanent water breathing, swim speed. You get the idea.
Instead of a new class, I would love to see the current ones branch out further - adding additional specs and doing away with the idea of a "pure" class - A rogue tank spec based around parry, deflection, dodging and a touch of shadow magic, warlock healing spec based around using their own health to heal others, or a ranged death knight specializing in the use of rune etching and raising the undead like we've seen with the servants of Helya, to name a few.
Rather than new races I would like to see further customization come to existing ones - new skin colors, faces, hair, etc. themed after the many sub-races found in the world(s).
If we do need a new race (and jumping on board the whole 'Naga' bandwagon for this one) perhaps we do see the Naga become playable - but not as they have appeared in game thus far. No, those Naga are the creatures of N'zoth, corrupted and twisted - but what if a select few have begun to doubt their Queen and her master? Doubt so deep that it pulls them into action against their Queen and perhaps a small release from the corruption of their brethren.
I envision a starting experience in a "naga only" environment like the goblins where you begin as a full naga - the type we have seen throughout the history of Warcraft, but through the starting experience you rebel - and perhaps even use an artifact or magics to break yourself fully away from N'Zoth and Azshara. So much so that you recapture some of what you once were. A full humanoid creature with features that are one part Naga and one part High Elf - scales and fins and wild coloration but built onto a body frame similar to the Nightborne or Night Elves with legs instead of the serpentine body. From a lore perspective it would certainly set the two apart from one another - but from a technical perspective it would also allow for existing armor and animations to continue to be used for the race. Obviously it would be neutral until a faction is chosen as part of the story line.