One day I’ll make a list of all the things Blizz said wasn’t going to ever happen
IMO the easiest and least disruptive solution would be to allow mixed faction premade groups in dungeons, raids, and other group content. Also, add mixed faction guilds like in ESO and FF14.
Make a raid tier with several bosses that have painful mechanics which are trivialized by an alliance racial. The 'ol reverse Tomb of Sargeras
Sense it swings back and forth. Depending on expansion. Sense alliance freaking out after having two an half expansion to themself. BFA I honestly can say it favors no one and primary against the player. Let make them mad and just have for horde. But a long time. Do not cave live WOD and Start of BFA.
Get rid of the faction divide. BOOM! Doesn’t matter any more who’s on what faction anymore. Play with your friends no matter the race they choose. The hall of fame doesn’t need to keep track because there won’t be any horde or alliance guilds, there will just be guilds.