I voted gameplay because:
-(As i ve understood), gameplay variation takes less time to develop.
-Content is pretty useless without good gameplay implementation (just think at tank-only maps and the actual use of transports).
-Now, with the transport vehicles there are a lot more gameplay possibilities.
-When a game becomes old, people buy it because of the quantity content or because of gameplay. However, in RO2 it doesn't seem enough easy to bring in content, and it's main strong point is gameplay, so I think it'll be easier and more successful to point on it.
I know that there has been a great lack of content, so everyone may think yes, more content again!, but, before voting you should note that it is pointless without a good gameplay implementation.
PS: sorry for my english, i know it isn't so good.