Its very likely to be just flags to stop on-foot in horizon ... frankly, thats not unusual for DLCs.
(the code is often in the main code base of DLC, and the DLC just unlocks it)
this is why its surprising Horizon 4 and Odyssey are not in the same instance.
I suspect there is some issue with that...
perhaps they didn't want horizon players entering (odyssey) conflict zones and shooting from ship/svr...
(though I can't really see issue there, since if this is possible, then its also possible in odyssey)
it be nice if frontier articulate the reason... just so we understood...
since as players, it 'appears' (but likely isn't the case) , you'd just have to stop horizon players from exiting ship and svr,
as this would stop them getting missions too (since they cannot reach terminal)
hard to say.. Id assume mid-term the plan would be to make odyssey part of main game (as they did with horizon) , and then ditch 3.8.
so , perhaps they don't want to expend too much dev effort on this intermediate state.
some odd decisions from player viewpoint...
but indeed the more you look at what's going on and has been said, it makes a bit more sense from the devs view... which seems to be, horizon 4 is just to get everyone on 4.0 client base, and hope that seeing it works ... and then paying the extra $20 (or whatever) to upgrade to Odyssey. once the 'majority' are over, then axe 3.8, so they can move forward.
(and of course, the story line being on exclusively on 4.0 is also the added incentive to get players to move)
tough calls, for all... but I think as players we all know the future is odyssey... and give the frequent sale price, its not much really.
sure, they can never hope to please everyone, and many have very valid concerns.
but from a dev viewpoint, you have to move forward, and concentrate efforts improving the current 'platform'.
(the consoles being dropped, is another indication this is the current thinking /plan)
anyway... I look forward to what frontier have in store next on the current storyline