I think Montoya has a very good point: In a normal MMO, you'd be sick and tired before launch even if they throw some new content at you.
However, as much fidelity and content as SC has, I think the real strenght lies in the "build quality" of the mechanics/gameplay itself.
To give you an example of a profession many "gamers" may find boring: Transporting.
I can pick up anything from a Aurora/315p/Avenger Titan and do small hauls inside a safe system... or blase eyes closed trough the most dangerous space for high risk / high reward jobs.
Or I can be more conventional with Ships like the Connie Taurus, Hull B, Freelancer Max...
Or I can go batshit crazy and go with a Hull D/E.
Or I can use a Starfarer, snatch fuel from gas giants and sell it with not upfront costs.
Or I can use a BMM, directly plant it on Planets and Trade.
I can do that alone, with escorts, in convoys, at the fear of getting intercepted by Pirate NPC or Players, hostile Aliens, upset tax collors or Space Whales.
And how much I make or lose from it depends on how well I do it, no handholding that will give you millions of credits to advance no matter how much you fail.
I know it's daring to predict the future of Games, but I'd say your "Truck Simulators" will not reach this quality in the next 20 Years.
To move to a more popular Genre: FPS.
Battlefield 1942 (2002) to Battlefield 1 (2016)
COD (2003) to CoD WWII (2017)
CS (2000) to CS:GO (2012)
We're looking at 12 to 14 years of progress in the most popular Genre, by the most renown publishers and all that really changed are the Graphics, which are set to ultra-low by the "pros" anyway.
Starmarine arguably does the same thing already.
The PU will allow a FPS Player to dropped in any place in a universe that's far bigger than every map of every FPS Game combined.
Not just that:
You can board or defend any kind of ship Ships, from Players or NPC.
You can fight, defend or just derp on Planets, Stations, Ships or wherever you want..
And there will be all kinds of suites between light and mechanized, ballistic and energy weapons.
You can be the evil pirate, good guy, mercanary, bounty hunter, assassin or futuristic monster hunter.
Or put simply: you can be whatever you want, doing whatever you want, wherever you want, whenever you want.
Again, I don't expect BF, CS, COD or whatever to get to such a level in the forseeable future.