SWTOR's PvP is quite good right now. Open world PvP in Ilum is good, excluding the bugs and exploits that benefit some player, is actually what it was advertised. Big, open war. The truth is, Rated WZ will do wonders for the game and will attract more players. Even better, a small scale PvP that would be ranked would provide a big time sink and also create a good competitive environment that'll push the game to a better experience. I suggest an arena ranked and unranked battleground where people will fight in a deathmatch.
Only one bracket should be made. A 3v3. You can balance the whole game around arenas and most of the times what is balanced in a small scale it will also be balanced in the large scale. 2v2 is too individualistic and very limited. Instead of creating some healthy competitive arena, 2v2 would be actually be a combination vs combination that decreases the skill and creativity required from the player and would lead to a huge flaming and crying forum outbreak where people will demand from the developers to adjust the game to their class' combination. 4v4 even though would be ideal since the whole game was build in the number 4 in mind it would not work in arenas. 2 healers and 2 dps or 1 tanks 2 healers and 1 dps would make really slow and long fight. On the other hand 1 healer and 3 dps would make zerg battles that would be frustrating and unsatisfying. 5v5 and more is just overcrowded, zergy and messy. 3v3 is optimal, the base of the mmo genre and the holy trinity. Tank, dps and healer or 2 dps and a healer would make a fight last enough, won't be crowded and every member of each team can coordinate without problem.
Balance the PvP around 3v3. The problem for the developers is the performance some classes have between PvP and PvE. Instead of nerf and buff every time, just give a bolster to dps in PvP if healers are overpower or on the other hand put a debuff of the healing received. Exactly what the devs did with the Trauma debuff. It's obvious that you can't balance a game around PvP and PvE at the same time with the same damage and healing multipliers for both.
As for the maps, don't make anything more than a basic, normal arena map. Avoid eruptic cannons, flame that rise every 5sec. No RNG elements in general. Let the best team win, with no luck involved. The winner should be decided by his skill, timing and coordination. Also avoid a map with many different leveled platforms. Being knockback to the ground to run up to the platform to be knockback again is not fun. Put some platforms that are easily accessible, some crates or other items that could get in the line of sight and maybe a pit of acid like in Huttball. Please make functional maps that will allow for competitive play.
I have to add here a little something. Make interrupts/knockbacks/standing up instant! Make it happen at the beginning of the animation so it would land as soon as the player wanted. The server lag, the internet lag, the human reaction time are already making it hard to land a interrupt. Having to wait for the animation to end, that means almost a second- only makes the things worst. Also, sometimes if I'm knockdown from an Operative in to the pool of acid in Huttball, I find myself dying not because of his attacks, neither for the damage from the acid. He throws me down for 1.5 sec and it gets 0.5-1sec to stand up. Please, make it so I can react instantly to the attacks of my opponent and not be restricted because of animation. A lot of people are raging about giving Imperials a lead. For example, It seams that Telekinetic Throw has the object that is threw to hit the target for the damage to be dealt where as the sorcerer's counterpart Force Lightning is instant. Same goes for some Bounty Hunter's abilities in comparison to the Trooper's ones. If it's just an animation thing, it's easy for you to correct it. To be honest, almost all of the abilities should has damage be dealt at the end of the animation. Especially for PvP, gameplay should be an priority over animation, so please, make it so.
My final suggestion for PvP is an introduction of two new type of Warzones. The first should be Team Deathmatch. People really like Ilum because it gives them the chance to play against other players without any other goal than killing or be killed. I believe it can be easily constructed and would be a huge hit from the community. Two teams of 8 people, 100 tickets, each death cost a ticket, first team to reach 0 tickets lose, no PvE element involved. Simply enough. You can add two chokepoints, like a bridge or a cliff and if you believe that would be helpful for more strategically playstyle, add two bases that would provide a 5% bonus to all damage and healing done to the group that controls them. The second one could be a map like League of Legends or DOTA. Two bases, each with an Inner Sanctum to the center, and only two or three different paths that connects them. Every faction has 3 turrets along the paths to their base to protect them. The winner is the team that gets to destroy the Inner Sanctum of the enemies' base. I'm not sure if it can be implanted into SWTOR but would totally make a lot of people happy and willfull to try PvP.