Not sure I agree with the Destiny comparisons... Destiny's season stuff has raids and whatnot were you are all but
required to have a large team. (I don't play it won't assume I know the actual requirement. I just know this stuff because everyone once in awhile people solo it and its a big deal on some news sites)
I, myself, would compare it to Diablo and/or Borderlands, were the loot/difficulty seems to scale up if you have more people but its completely playable alone.
More info on the expansions:
Expansion I: Underground
This first major expansion opens up a new area to players as they explore the uncharted underworld of New York City
with up to 3 friends for intense co-op action.
Expansion II: Survival
In this expansion, players will have to survive as long as possible in a very hostile environment that will challenge even the most talented agents.
Expansion III: Last Stand
Stay tuned for more information.
(
link)
The above seems to be very consistent across all news sites so its likely true... One site made mention that Survival would turn the whole map into a DZ like area. Another mentioned it was a mini campaign. A couple said you had to complete the game to access it. None one seems to have any news on the Last Stand expansion.
Footage of the first expansion... (I think?)
https://www.youtube.com/watch?v=nvwh6JN-rsU
But, what if the game has multiple season passes...?
I think this is what you were wanting to know... The Gold version is the base game with the season pass.
According to
Game UK the season pass is £29.99 or something like $45 USD. (USD price doesn't seem to be official yet... I guess neither is the UK's price since its one site.) Actually,
Gamestop has the season pass for $39.99 USD.
Strangely no place is selling the season pass by itself on PC yet.