What can be done to keep SWTOR strong?

I feel the answer unltimately to the dwindling subs is endgame, a term that is foreign to sandbox games. Although everyone gets there in there own time, the results once there seem to be predictable.....they quit.
This is sadly where themepark style games are weak, it is fair to argue Sandbox games never attain a real large base to begin with, but a merge of the two may be the ballance we need.
I would urge Bioware to consider more content inline with the freedom, exploration and creativity a sandbox has to offer as they have already put forth an amazing themepark.
This may seem confusing to players who pvp to 50, but anyone who spent the time to playout the stories on each planet to level would agree. Alot of work has been done to create vibrant, living worlds, now we need ideas and suggestions for us to visit them, repeatable missions aren't enough.
Those who have played other games long term please feel free to offer your insight into what kept you there.
I used to spend hours in SWG looking for starship parts, farming parts for my saber, decorating my homes and ships, engaging in open world pvp, ect.

give out more free time to add the subscription numbers.

I was thinking more in terms of keeping the existing player base, adding new ones is always ongoing.
Any game additions or changes you would like to keep people playing at 50 and interested in the bulk of content already ingame?

Rateds and being able to customize the skin of your gear whilst keeping stats.

I'm willing to bet the majority of the players aren't level 50 or legacy rank 6,(so didn't get the free month) you can keep spewing that garbage though if it makes you feel better.

Only on the internet is the act of giving people something for free considered a bad thing.

These are not in the order of importance, just in what order they came into my mind:

1. Stop destroying things people have spent time on. A lot of time had been spent to get centurion gear, now not even worth what you get from vendors. Lot of people spent time to get battlemaster title only to see everyone get war hero after Ilum failures. PvP commendations is exactly same story. Maybe it is just me, but this sort of things make me lose interest very quickly.

2. I listen to the podcast and I hear them giggling while implementing totally useless stuff like rocket boots or the whole legacy system. Prioritize "things to do that lead to rewards" in the game over novelty features. To be fair, some good stuff have been done like responsiveness fixes and probably some of the pve content (I dont know about ops, I dont do them). Also legacy might become something cool, but right now you could delete it from the game and it would not have any effect on my playing.

3. SWTOR is a direct competitor for WoW so atleast compare your features against theirs when you implement them. Ilum type "outdoor" pvp has been done in WoW and there has been much of the same problems and solutions. I'm not saying wow is the perfect implementation of everything, but there are lessons to be learned.

4. Accept the declining interest in the game and merge servers or something. My server seems very quiet.

5. Open up an API for addons. People like different things and the basic UI will always be lacking for some players. Addons also offer change when you get bored of the UI so even if the default UI would be great, it is always the same.

6. Make dueling something people can do. Good example is wow, where do you go if you want to duel or watch duels? Outside of orgrimmar (atleast this was the case when I played years ago, dunno if it is anymore). If I am at the fleet, I have no idea where to go duel. Should I go to some arbitrary planet and bring a friend?

7. Remove fleets and replace them with planets. I want to see the other side killing me in my own capital! This would also fix the issue 6 if you could just go outside to duel.

Wouldn't forcing players to sign up for a 1 year deal to get SimCity 5 and a mount for free, be a more legitimate way to add to subscription numbers?

more sandbox relate content.

Fire every single person on an existing development team and get someone who is not brain dead instead.

The undeveloped space content would be your best bet. I don't know how they can add sandbox elements to currently existing planets.