the only thing FD can be held responsible to is what their store says... and it says nothing about adding missing content to the main game, it only says about bugfixes and small tweaks
Well it's not black and white but I do think core game features will be expanded for base ED players. ie new missions, the depth of the current missions, new mission mechanics and so on.
The thing is there is only one ED "galaxy" and all players share it, if (for sake of argument) a new ship is added for season pass players then it simply must be added for base ED players, if that's not done then you start to run into all sorts of issues which then have to be worked around. Yes it's possible it might not be flyable but it must at least be in game and viewable as a ship model flying about.
The same with other mechanics, it will often make sense to just add it to core, in that it would be too complicated and require extra work to make the galaxy behave differently for season vs core only players.
Planetary landings is a clear exception to this since it can easily be walled off, other added game mechanics not so easy.
If say a huge alien generation ship is added to the game, what are they going to make it "invisible" to core players? Not likely.