We know they are exploring mixed faction raiding and grouping etc.. to be honest, i think they should go much further.. they have to find a way of opening up more of the races to both factions without losing uniqueness of the dual faction system. Here is the best way to do it.
**EDIT**
TLDR - version
1. If you are a player, you can play for whatever faction you want. Group/guild/raid with whoever you want. However you make your character and start in the traditional faction, before the choice to choose comes.
2. In the lore/story - only humans/gnomes/dwarves are alliance exclusive and on horde Orcs/Trolls/Tauren - this doesn't affect players (players can still choose any faction), all the other races have left the faction unity, and are doing their own things. New friendships and enmities exist on a per race bases
Here is one way of fleshing the detail of what happened to the races in lore.
- Open up some races to both factions, but keep some races core off.
- Open up raiding, grouping to faction team ups.
- However guilding would require a changing faction with your character - yes if you can join a guild in the opposite faction with your race, even if that race doesn't work with that faction - it's an individual choice.
- Lore is important, so the factions are still going to be important, but how the races do them will change Dramatically
Race wise Humans, Dwarves, Gnomes, and Orcs, Tauren , Trolls are staunch loyal to the alliance and horde respectively ...and this is where all the faction drama mostly remains.. other races have rivalries , but also friendships based on sub-factions, and is dealt with on a per-race basis.
But everyone else can now choose either. For the faction locked, you can still join a guild of the opposite faction, but you can't change your faction.
For the races who can choose, once you choose your faction, it's final on that character (that's why paid faction change remains), however you can still join guilds of the opposite faction with taht character.
Here's How
Kul'tirans - the pirate faction is friendly to the horde
Worgen: night elf worgen and Val'Sharah worgen are friendly to the horde
Night elves: The night elf playable faction (the Darnassians) no longer care about the factions - they view the alliance as unfaithful and the horde as morally weak - but they don't stop individuals joining either - night elves who do aim to "restore" their faction. Highborne night elves actually want to lead the races rather than retreat from them so you can role play as one of them actively joining either faction to help lead or guide. Night elves should be developed as faction anyway
Lightforged - focused on the goals of the Light, unlike the first Draenei to contact Azeroth, they aren't picking sides, the Light wants EVERYONE. Lightforged develop a very close friendship with blood elves, building on the shattered offensive with normal draenei.
Void elves - although Silvermoon still doesn't want them near the Sunwell, yet they are the only ones that can protect it from Ethereal void incursions which will surely return, some blood elves know this and void elves sometimes ally with the horde to be in a better position to help
Blood elves: Blood elves are horde, but high elves are alliance - same race, same options, you can choose your faction, if you go alliance you're now called a high elf. Thalassians have generally drifted away from faction fanaticism and loyalties, they help out but pursuing magical themes like the light with Draenei, and the arcane with nightborne from the kaldorei empire are where their future lies. As a long lived race, the blood elves have looked well beyond the horde, the horde isn't their making nor their responsibility, it's a young faction spearheaded by a very young race (the orcs), building a racial future on it, is not a priority, they help for now, securing magical mastery is far more important, hence the close allies with Lightforged and nightborne.
Forsaken: After the vents of the BFA prequel novel , Calia Menethil, there are humans and forsaken willing to work together. Some forsaken are happy to fight for the alliance, even though acceptance is few and far between. No more Sylvanas re-enforcing the horde, . While most forsaken are with the horde, because most humans reject them, this isn't always the case, in especially in Lordaeron now, a lot of families have come to accept their loved ones in this new form, but still many do not.. this is a very interesting dynamic to explore that faction limitations prevented. Undead , like night elves above, should be developed as a powerful faction, although as a player you pick either the horde or alliance.
Goblins: Bilgewater are generally horde friendly, but like all goblins, they care more for profit, and don't care about batting for the other side, , however uou can now play as a Steamwheedle goblin too, there is no aesthetic difference on the goblin model between Bilgewater and say a Steamwheedle cartel, you can pick whatever side you want.
Mechagnomes: Mostly bat for the alliance because of the strong gnome connection, however, the horde helped out, and they are more interested in knowledge and technology, as long as the horde is also open to their ideas and experiments, there are enough Mechagnomes who don't mind fighting for them.
Vulpera: Started running into a lot of issues in many lands once they could leave Zandalar, and actually found a lot of alliance races full of mistrust for them and their thieving ways, however, they got on very well with rogue guilds, black market ops, and they are viewed like how some countries view gypsies a noisome pest, they aren't organised, so the Vulpera aren't with anyone, Vulpera can choose who they work for.. after approaching the horde, it was quickly discovered that the leadership acceptance of the horde was pretty much only applicable to the Vulpera there at the meeting,
Turns out they only demonstrated the usefulness of the race, as for loyalties, well that's an individuals thing.
Zandalari: Have stepped back enormously from the horde, Sylvanas' scheming that lost them most of their fleet, lost a war against the alliance, in fact where is this help they needed? with Uldir under control and N'zoth defeated, the horde is more trouble than it's worth, and they hate the alliance. Still isolation isn't an option. Zuldazar is an independent kingdom, but both alliance and horde can go through it, and Zandalari trolls can fight for either faction. However you're looked down on if you choose to help the factions, especially the alliance, but many Zandalari who do, do it for power. It's much harder to get on with the alliance as a troll than the horde.
[If there were two allied races that would be faction locked, it would be Zandalari and Mechagnomes]
Mag'har orcs have a contingent of Lightbound who preferred the alliance, but also Shadowmoon who were drawn to the void elves (who whie technically work both factions are officially alliance)
Highmountain Tauren: This one is easy, they've got on well with kaldorei types, nightborne and night elves are something they're use to and never had trouble with, the friendship and separate lives continue... Highmountain druids are a much bigger thing in their society and their influence allow as night elf druidic friendship - though Darnassians aren't alliance bound anymore and this is more tied to druids than all Darnassian night elves, Val'Sharah works a lot with the nightborne, their peace with kaldorei druids opens up a door for Tauren into alliance societies and cultures, though this isn't common outside the broken isle and thus outside the night elves.
Have I forgotten anyone? Remember Stormwind humans, dwarves and gnomes are alliance locked. Orcs, Tauren and Darkspear trolls are horde locked.