Instead of a full 4th spec, they implement...
Multi-Classing
Now, sure, not a new idea, as many many other games have done it, but it would fit just fine in today's world.
Once you hit a certain point/benchmark/gate/whatever, you can choose a second class.
That class will respect race restrictions and remain within your Armor Class tree.
Once you unlock it, you visit your class trainer to swap over to it, then you get the full kit as that Class.
Yep. Simple, yet straight forward stuff.
So a Troll Mage could opt for a second Class of Priest.
Now that player can be either Mage OR Priest, but only one at a time.
But, what's the difference from every other thread about Multi-Classing and every other game that does it, you may ask?
Bake in the Druid 'Affinity' talent methods into this as well.
That means that, while this player is a Priest, they get access to select Mage spells, and vice versa.
I think the Druid Affinity ability works well as it fits thematically with their class being a 'jack of all trades'.
Expanding upon that to let players be a second Class with cross-over sounds like it could be interesting, add new playstyles, weave in situational/rotational abilities, and basically just freshen things up a pinch.
Because you stick within your Armor Class, you don't need a full new set that can only be used with a single Class.
Weapons may change, sure, but we already have that today and many classes share already within their AC group.
Now that Mage above would have access to Renew, Heal, and maybe Shadow Word: Pain, for example (one baseline ability from each spec).
They won't be as strong as they would be if they were the Priest/spec themselves, just like Druid Affinity spells aren't as strong either, but they would be additional options to weave in, with renew/heal being a self/other backup (both useful for solo and group activity when you may range your healers) and SW:P could even be weaved in rotationally because, even though it doesn't tick as hard as a Spriest's one does, it's still an instant cast DoT for on the move, etc.
Of course, they would need to be careful with the crossover abilities to make sure you don't inadvertantly give someone too much utility or otherwise create a bigger balance problem, but more so some general yet basic thematic abilities for crossover to mix it up a bit and add some situational flavor.
Anywho, what do you think of an Affinity-style application to Multi-Classing?