I’m not going to argue for an entire change at this point, but I will point out why 1.12 is actually not really a good version of vanilla wow.
-1.12 was released august 22nd 2006. This brought naxx, new av, cross realm battlegrounds, some class balancing (edit - my timeline on naxx was off. It came out 1.11). By this point mc and most earlier content was nerfed, classes were buffed. Battlemasters were added in cities, and auction houses were no longer just in ironforge and orgrimmar.
-2.0 was released december 5th 2006. This brought arenas and removed the old honor system, basically letting people buy any gear with honor points. Note that this is about 4 months after 1.12.
-Tbc released january 16 2007(about 5 months after naxx released)
Main points to consider:
The vanilla honor grind existed with cross server battlegrounds for about 4 months. Vanilla cross server battlegrounds existed only for about 4 months before arena came out. People only had about FIVE months to do naxx. That means potentially 20 clears of naxx roughly, POTENTIALLY, and that’s it. That means only 5 months of naxx gear if you were a bleeding edge guild.
With naxx gear, people can just completely obliterate you in bgs. TBC was coming so soon after that it did not matter - not everyone was able to clear naxx. However, if we are sitting in naxx gear for a year or more pvp will get REALLY bad - there is no resilience, so people will be hitting for insane numbers. After two years or so it will be all about oneshotting in pvp.
XREALM Bg’s - The vanilla honor grind was NOT primarily done under these conditions, by the time they were released most people who wanted to do it had gotten their ranks and AQ gear was more available. Xrealm bg’s killed the pvp community on most servers because before them you knew who people were on each faction. If you look at alterac valley on beta, cross realm is very similar to that experience - you will not know anyone and there is no incentive not to just afk or bot. Battlegrounds are FUN when people CARE - with cross realm people will not CARE about battlegrounds. This is the key to it, queues will be short but they will not be something people care about since they do not know anyone on either side.
I have heard people argue that they still knew people from their battlegroup but from my experience this is bs. I would see a kelthuzad premade and say on vent “kt premade” - I did not recognize any of the individual players or guilds and I grinded pvp ALL day.
Edit: I guess naxx released in 1.11(late june). I made a mistake on the timeline, but the general point still stands.