Blizzard didn't change the talent system. Classes will be exactly the same, the only difference is that instead of 3 Azerite traits you can choose you get only 2 when you choose a Covenant, and the Covenant system is a much more unforgiving one than even Azerite gear.

If you play a hybrid class, for example, you're completely screwed, because you'll simply never get to play more than one role, since the Covenant traits are only suited to one role per class.

For example, let's take a Paladin and Bastion, which is the Covenant they gave us more info about.

Bastion's Divine Toll (Instantly cast Holy Shock, Avenger's Shield or Judgment on all valid targets within 30 yds (based on your current specialization)
6,000 Mana, 30 yd, Instant, 1 min cooldown) is great for Holy in any and all situations because it's basically a huge AoE heal.

For Ret and Prot, on the other hand, it only works for huge pulls. It's useless in a one or two-boss fight. Like, completely useless.

What happens to the Paladin that raids Holy but eventually - say the devs screw the pooch and nerf Holy Shock to oblivion - wants to change spec and go Prot or Ret?

They are forced to change Covenants, but changing Covenants is not supposed to be as easy as changing a set of gear. They'll probably have the same issue people had in TBC when changing from Aldors to Scryers, which was having to gather a stupid amount of resources to grind rep all the way down from Hated.

I am very underwhelmed by this system.