Heh, nice... First real feature request...
1. Of course it can be implemented.
2. Not a week or two. Probably 1-2 months... There are two ways to implement it:
a) Write a PPPoE SANA-II device from scratch.
b) Take a PPPoE implementation from *BSD and integrate it into the kernel.
I guess (b) is prefferred since there's no need to write anything from scratch and in-kernel PPPoE is more efficient and would be easier to set up. IMHO SANA-II drivers are designed for hardware abstraction. Protocol abstraction is simply not their job.
Currently i am unable to write the support because:
1. I don't have time.
2. I don't have good testbase.
It is possible to raise this topic again. The project becomes huge and it can be divided. I would suggest to break it into subtasks. Implementing PPP and PPPoE (they are linked together) could become one of these subtasks.