Well your ultimate goal is to become "Elite", and you can get the elite rating in different categories as trader, bounty hunter, assasin, pirate, miner etc. Basically that is a grind, because most probably gaining rating will be slow whether you are a good or a bad pilot.
I also hope there will be accomplishments for helping out factions like the federation, alliance, or independent star systems.
One of the great things is also the mission generator, that is based on the evolving universe. If a planet has a plague, you'll get missions to get medicines. If a new space station gets build, you can help with the construction or hinder it by helping parties opposed to the new space station. So there will always be something to do.
But nobody really wants the "hamster wheel" mechanic that WoW established. If the gameplay gets old, you should either quit or set your own goals, besides the elite rating. The devs could add new higher level equipment etc to earn but that would just be more of the same old same old. Playing the same game mechanic just for new purple items can be fun, but burns people out. It's not really rewarding, it's an unnatural and unhealthy gameplay style. I'm sure there will be some of that, equipment you will only get when advancing in a certain career or something like that.
But generally the devs plan to add actual new gameplay, new things to do and achieve in the universe, instead of just adding new content. Instead of "more of the same" you'll get new gameplay mechanics that actually makes the game more complex in a fun way.
Planned extensions include first person activities (boarding other ships and space stations) and seamless planetary landings (big game hunting was mentioned for example, maybe you'll be able to build a zoo later?). Adding new gameplay is of course a far better approach.
Themepark games like WoW or SWTor can't really do that, because they have to model and create every single level. The procedural generation allows for far more flexibility. A single new rule for generation can affect the whole universe and make new gameplay elements really work throughout the game. Maybe we'll get spying missions on space stations? We don't know yet. But the technical approach and vastness of the universe allows for far more things. Theoretically you could blow up a space station, the game could still work. In themeparks, you can never kill the messenger, because then you couldn't complete a quest or something.