At this time, R2-D2 is the only confirmed character for Star Wars: Episode VII. R2 is undeniably a fan favorite - he has always been the decisive, witty, and energetic droid in the Star Wars universe. Being an astromech that belonged first to Anakin and then to Luke Skywalker, he’s often on the front line of battles or at least in the thick of excitement. R2 is suited to those tasks and to the danger and glory that is war. But let me go out on a limb and say something that may be an unpopular opinion: we need C-3PO in the sequel trilogy.
Threepio’s humor comes not from bumbling cowardice, but from his inability to fully understand his human companions...
Unlike Artoo, it’s easy to discount Threepio as a viable hero. Threepio is a chronic worrier who would much rather spend time in a museum over any kind of spaceship. He’s programmed for translation and etiquette. I’m sure many fans out there agree with Owen Lars and think that we “have no need for protocol droid.” But however uptight he may be, Threepio is an important character and not just as an opposite to bounce off R2.
C-3PO can communicate in Basic, as well as six million other forms of communication. In A New Hope, Threepio diverted a group of stormtroopers away from Han, Luke, and Chewie which enabled them to rescue Princess Leia. Soon after, he enabled his and R2’s escape by lying about R2 needing maintenance. Artoo may have had a another solution for the situation, but it probably would not have been as easy. More than once, Han uses C-3PO to “talk” to the Falcon to figure out what is wrong with the ship. Although he participated unknowingly, it was his ability to speak Huttese that assisted the plan to spring Han from Jabba’s palace. Whether you like Ewoks or not, it was Threepio (and his status as a god and skills at storytelling) that won the creatures over to the Rebellion’s side and allowed the successful destruction of the second Death Star's shield generator. People who have been around R2 long enough are able to understand him well enough without translation, but Threepio enables the duo to be able to instantly liaise with life forms.
There are things that R2 can’t do, even with all of his attachments. It’s commonplace to see protocol droids around town running errands for their masters or working in various shops and venues. They are humanoid, can interact with other races fairly easily, and are generally trustworthy in the public’s eyes.They fit in anywhere from street shops to the highest levels of government and royalty. In the duo's adventures, this makes Threepio very useful. In the New Jedi Order book Rebel Stand by Aaron Allston, Threepio is fundamental to R2’s plan to spring Han and Leia from an undeserved jail cell. He escapes from an enemy occupied Millennium Falcon, is lead through town to where they are being held, and delivers a sack of important food stuffs (Leia’s lightsaber and Han’s favorite blaster) that allow the couple to break out. As clever as he is, R2 could not have done it on his own.
C-3PO seems in his element when he can work with his astromech counterpart, but he can also can be shaped into a protagonist on his own. He is a hero who doesn’t know he’s a hero; someone who doesn't seek glory or recognition for his contributions (maybe just an oil bath or program upgrade). He is often put into dangerous situations completely against his will. Yet in these tight spots he will always assist, even if it's contrary to his preservation programming. In the plan to rescue Han and Leia that I brought up earlier, Threepio says “So this is what bravery is… How odd that it feels like petrification,” [1. Allston, Aaron. Rebel Stand, p. 143]. Yet he still follows through, not sure if he is even able to get the job done, because it is his duty to aid his family. His unwavering support, even in the smallest ways - like being a nanny for the Solo children - contributes to the greater good. Besides his freshly oiled lacquer, this is how Threepio shines.
The Threepio we need to see in the Sequel Trilogy is the protocol droid of the Original Trilogy who was fleshed out in the Expanded Universe. He walks the fine line of annoying uncle, court jester, and loyal aid. He can move along expositions and provide lightheartedness while still contributing to the cause in his unique ways. Not everyone is an unstoppable Jedi Knight, a talented politician, an unbelievably lucky rogue, or an extremely clever droid with a dozen built-in tools. C-3PO is that character who doesn’t seem special, or even likable, but proves that even the most unremarkable people can do extraordinary things.