As Blizzard stated they're looking for an idea to solve server imbalances and low pop servers. Now, I know what you're thinking, "just merge servers and be done with it". but merging servers gives issues that requires new tech to solve. for example, they would want you to keep your friends and ignore lists, and if someone has more than 11 chars on a server, they'll need new tech to solve that. in addition, server mergers are only a temporary fix. inevitably, you're going to have new low pop servers emerge. you also need to figure out what servers you're going to merge, because if you're not careful, you're going to create or increase faction imbalances.
my idea to solve this is as follows: mentor servers. please read the entire description before you complain or say you stopped reading at X.
it's basically a combination between CRZ, instances and server merges, but attempts to address the issues that both present.
low pop servers and imbalanced servers are assigned mentor servers according to criteria like faction balance, PvP style and content progression. multiple servers can be assigned in both directions, but it remains contained to small clumps. once assigned, these servers remain separate entities, but can interact with each other completely. players stay on their own servers, but they can do anything they want with anyone from their mentor server(s), as well as anyone from the other mentored servers in their clump. to prevent massive overpopulation, these clumps don't simulate a single azeroth, but multiple azeroths, like The old Republic did it.
for example: server A has 100,000 Horde and 17,000 Alliance, server B has 2,000 Horde and 19,000 Alliance, server C has 10,000 Horde and 62,000 Alliance and server D has 3,000 Horde and 17,000 Alliance. these are just numbers i've pulled from my ass to give an example btw and are likely much higher than actual server numbers, don't look for anything behind them. it's clear that these servers are either imbalanced, low pop, or both. When the mentor program is rolled out, these servers form 1 clump. in total, there are 115,000 characters on each side on all servers combined. Characters from any of these servers can play with any character from another server as if they played on their servers, like an extreme version of cross realm zones and grouping, but without the need to have a player from the other server as a realID or battletag friend. a normal friend suffices
now, you probably are going to say "but Scrooge, 115,000 characters is going to cause immense lag and competition for quests and professions, as well as ruin the AH. the game will become unplayable". that's solved by semi-instancing. for every 5,000 players online at the same time (again, numbers can be tuned for real population values and live values can be 1000 for example) on each faction, the server clump creates a new instance of the game and redistributes all players across all instances, keeping groups and guilds together and attempting to perform a redistribution that will not interfere with normal play. this means that generally players that can see each other can continue to see each other, and players that were engaged in combat with one another can continue to fight during the transition. since this tech is based on cross-realm zones, it will not give a loading screen, but maybe some lag. this way, everyone can keep playing normally and shouldn't notice more than a small lagspike.
players can freely move between these instances, interact physically with anyone from their instance and interact using directed chat with players on other instances if they know their name and server. inviting another player will automatically bring them to your instance. if an instance has problems and goes down unexpectely, players are temporarily spread over the other instances while the server clump generates a new one if needed. if this transition isn't possible, only the players in that instance are affected.
multiple instances share the same auction house. auctions are assigned to an instance when they are made and don't change when the player transfers, although a player can post an auction and no matter what instance the buyer is on or what instance you moved to since then, you'll get your money. players can browse the different instances to see if there's a rare item they want.
cross realm invites continue to work as they do now, and players can keep inviting friends from other servers, even if they are on another cluster.
So what does this solution achieve:
1) communities and characters aren't affected by this change. noone will need to be renamed, noone will need to pay for a server transfer (unless they wish to leave their server cluster) and server communities stay loosely together.
2) population and faction imbalances cancel each other out, because the population from multiple servers is spread over multiple instances. each instance will have a relatively equal amount of players.
3) auction houses will be more flexible: you could buy out an item now, or see if another auction house has a bargain for that item. I don't see the average user do this for stuff like gems, enchants or glyphs, but a small subset of the playerbase will actively do resale between the different auction houses if there's an item with a huge difference.
4) competition for rare mobs, quest items, gathering nodes and other zone spawns which became much harder to farm after CRZ is smaller, because the actual presence of players is smaller. however, you can still switch to another instance if the competition is too high for you, or if it is too low for you...
5) players who enjoy low population will not be forced to go to a crowded server because of a forced merger, but will be able to enjoy the amenities and features that a more populated server offers better over a low pop server, like a more abundant AH, a wider pool for grouping and pugging, and more interaction with other players.
Now, i'm certain that some of you have a huge objection to the above. some of you will say that server mergers is the only right answer. but before you state your opinion on this, please think. compare server mergers to mentor servers, and ask yourself: "is there a problem that mentor servers have that server mergers don't have? is there an advantage to server mergers that mentor servers lack?" in addition, this is only a rough idea. the idea can be adapted and adjusted so that those problems and advantages are not as pronounced or even solved.