The system is so great and inspiring. Finally we have a way to express our identity by making a long term choice both when it comes to abilities and in the conduit system really and it feels like a tiny step in the right direction in making WoW a proper RPG again.
I think that Blizzard should use this as an inspiration to make subclasses in the next expansion. These would obviously have to actually be permanent for them to make any sense. You could get a handful of possible combinations where you merge your class with a different class and gain access to an additional fourth spec inspired by both (or 3rd/5th if you're a DH or Druid).
For example mages could choose from:
Spellsword (from merging with Warriors)
Illusionist (from merging with Rogues)
Void Mage (from merging with Priests)
* I take no responsibility for how bad or corny these might be, they're just examples in order to give you an idea.
On top of this they could add something like the conduit but perhaps merge them with the current talent system so it wouldn't become too bloaty. You could have lots semi-permanent parts that are cumbersome to change (either a CD like with conduits or have to find a trainer in the middle of nowhere) and then a handful of freely swappable parts that would act just like the talents do today, maybe three or four of those would be appropriate.
You could also gain access to a unique transmog and mount depending on your choice if you're into cosmetics, it wouldn't really give you much identity since you can just use something else but it would be a nice little bonus.
This would come with the added bonus of making it much more interesting when rolling a second or even third character of the same class because now you could make it different from your first one.