I was one of the people who was eagerly awaiting the release of SWToR and then was disappointed by how the game turned out.
I still hope BW will make some changes that will make the game worth playing. Here's what I think would be great. This is my personal opinion only:
1) Make space come to life -
The space missions in SWToR were the biggest disappointment for me. I think for the next expac BW should make space a priority. Ships should be bought for credits and upgrades should be drops from space bosses which you fight using your ships in space or by stripping enemy ships you just destroyed in glorious PvP bouts involving hundreds of players teamed up. In a nutshell, take the idea of space from Eve and integrate it into SWToR.
Space is what makes this MMO stand out from the rest and it seems to have been neglected completely. While some people would enjoy the 'on-rails' set up you get currently, just the thought of PvP space battles where 40-100 ships gun it out is exhilarating. Big, unforgiving bosses (example crystal entity from star trek universe or some things like that) which have to be taken on by raids comprised of ships would also give the PvE crowds something to work on. There would also be bosses which hide deep inside asteroid fields etc, so not only do you have to kill the boss..you have to navigate your way to it. I could go on and on but it's the universe, there is no limit to how much can be done if space was open and alive.
2) Art and architecture needs to be more space-y
No places in SWToR have the wow factor. I mean look at alderaan in the movies, it's breathtakingly pretty but in the game it just does'nt feel as well done. When one is talking about planets, let the imaginations run wild. Have architecture and art that actually feels like one is going into alien worlds. All buildings do not need to have the same basic concept, variations are good.
For example Hoth needs to be frozen but it can also have some great ancient ice castle carved out of rock and ice and has sporadic vegetation that thrives in ice climate etc.
Going forward, the new planets must feel alien and have the kind of effect that one got when you went into nagrand for the first time or when you flew to the top of the temple of storms in storms peaks or how netherstorm had such a unique alien feel.
3) It's a space game, it makes sense that I should have a flying mount/ship to fly on planets.
Seriously this is a no-brainer.
4) Give us the basic features and give 'em to us asap
Dual-spec, macros, mouseovers etc are basics. Sure some don't use them but any good dev would know, you'd rather have the feature in case people use it than not have it and have half your playerbase crying about it. Personally I think SWToR should open to addons because that saves dev time as community can build some great addons as we have seen with WoW.
5) Build a better overall story (not to be confused with class story)
BW must remember that more people relate to Star wars than KOTOR. Many people have no clue who Raven is/was. Bring in relatable elements from the movies into the story or create a story that we all connect to using quests etc and then wanna see it to the end and am sorry for quoting wow again but like how the burning legion and arthas stories were. The raghkul while okay is not really that cool. We need more illidans and thralls and jainas....heroes and villains who stand out and we see them regularly and want to know about them.
6) Take good ideas from WoW and Rift etc
Rift has produced some amazing content and so has WoW back in it's golden days. I would call WoW the master of all MMOs and it is no shame to learn from a master. Look at why WoW is so famous, see what ideas work and incorporate them in SWToR. Same with Rift, it has the content production rate pat down...aim for something like that.
7) Do something about talent trees now-
Once the level caps start going up, these talent trees will be very very bloated. Do what WoW did at Wotlk, do it now before this gets out of hand.
Once again, these are just my opinions and for context I leveled an imperial and a republic character each to level 60 before I quit SWToR.