I'd say Sammy and Joe are writing for it. I really cant see Jason filling in full time.....even though its rumored. RHCP and CF will work out a schedule i'm sure.
from what im told, the band will record it, and jason will fill in on tour, he's played with sammy before at cabo, and sat in iin vegas at the last chickenfoot show
Wouldn't be the same though. Jason is a good drummer, but just in a different style...I like the groove-style playing Chad Smith brought to the band, it's the thing that really made it a unique entity from all the other hard rock supergroups over the years.