Do I want Orochimaru to be the final villain (or at least a major villain again)? Definitely. Here is why:
1) He was the first major villain - would be nice to come full circle.
2) People have invested their time in him - getting to know him, love him or hate him. There needs to be a pay-off to see him either succeed or fall - in dramatic fashion.
3) As far as a villain goes, I still see him as being the best and most creepy ever produced on the show - from the voice, to the snakes, he is perfect. People discuss his lack of power - it is interesting to note that we have not seen Oro fight much at his full potential (without being sick, disabled or interrupted). Therefore, seeing him fight to his potential is a must. Finally for a villain who has spent a lifetime seeking out new techniques - who knows what he has up his sleeve? He is also hailed as being very intelligent - his plotting and scheming will hopefully result in something big.
4) His past death scenes have been disappointing - his weakened fight against Sasuke and the short confrontation with Itachi - both left the viewer wanting more.
With all of the above, I can't help but feel that we must see a 'proper' ending to this character. He is the villain that kept me enthralled throughout Naruto and through the first part of Shippuden.