At this point, we have seen:
1 vex raid
1 hive raid
Prison of elders (for all intensive purposes, since skolas is the big baddy, I'll call it a fallen raid)
And another hive/taken raid on the way
With a suspected vex raid following it
But nothing remotely cabal themed
Why?
I believe that the story has been set up as so they have to be more important later, but, as of current, they play little part in the story. The fallen actively attacked us, the hive were returning, and now the hive come for us
(I'm ignoring VoG because, according to some theories, our actions aren't acknowledged of completing it due to the nature of time in the vault...it's a different game theory)
The cabal however are passive. They've set up base on mars, with a supposed failed attempt to go for the moon (see: the cauldron) but haven't gone for us.
So?
My bet is that they'll be important once we've actually talked to the warming Rasputin.
Why?
Because I think Rasputin will have us go to Charlemagne's vault to...do something. Charlemagne was a known warmind, and the canal could possible be attacking it. I think a raid where we have to go rescue the warmind would be equally as cool as one where we have to kill a big boss, no?
[b]tl;dr[/b]
The games story means the canal won't be important until after we've dealt with all current threats. We could bring the fight to them for Charlemagne, but it won't happen until more story with Rasputin.
-
Far as i can tell the cabal do want to expand their empire but think only thing stopping them atm is the vex surging at them and fact we basically assasinated the top commanders on mars atm.