I consider myself a big Destiny fan and I think this is a huge ask from Bungie.
As a result... They will do something drastic. I think D2 will ship with even less story and lore than D1 every attempted. They know their core strength is gunplay, be it Crucible/Trials or PvE and raids. As such, I presume they will deliver story arc content piecemeal and slow. Of course I want to get a cut scene at the end of D2 second expansion where The Speaker takes us into the core of the Traveler, but I doubt this will happen. As great as the world is, a lot of its greatness derives from mystery. And since Destiny has a 10-year-plan, we will probably never get the lore treatment we want. Things will stay ambiguous and loose - indefinitely.
As for the Cabal angle: expected, but weak. We have seen Cabal since the beginning of D1. They have their strikes, story missions on Mars. They had some plays against the Taken in TTK, but were completely missing from Rise of Iron's narrative. They are the brutes of D1. As such, they are not a very charismatic enemy. Building a narrative around them might mean that the new Cabal assault force in D2 brings with it some unknown enemy instead. Imagine Cabal infested with Destiny's Flood or something.
I want to be wrong though.
We knew for a while now that D2 would have a big Cabal focus. Jason (I think) reported a while back that the development on a Cabal Raid for D1 was halted to be moved over to D2.
D2 will broaden up eventually just like D1 did, but in terms of structure I would not be surprised if the Cabal were for vanilla D2 what the Vex were for vanilla Destiny 1.