I'm sure Treyarch are happy where they're at.
I'm sure plenty of other developers would jump at the chance of developing a Call of Duty title every 2 years so they could have some of that profit in their own pockets.
There are other game developers/publishers out there spending more on developing games and getting fuck all in comparison back.
In short: Treyarch are financially well-off forever as long as they keep making Call of Duty games. Why in the world would you give that up just to "come out of infinity ward's shadow".
In my opinion I think their Call of Duty games suck in comparison to Infinity Wards. I loved COD2, COD3 was meh, COD4 was Awesome, Skipped World at War because it's Treyarch and had already learnt from COD3 and then bought MW2 on day one and it's fab.
Treyarch COD games are alright but they don't warrent a £35+ purchase in my opinion. The games are always full price because Activison are greedy and then always outdated within one year because the next installment is released. That is when the price starts falling.