I've heard the same theory. Jetstar will become all Airbus A320/A330. As such will keep training costs and engineering costs down. The airline will be able to transfer crew and engineers between aircraft cheaper and easier depending on the short term needs.
Qantas is telling the world Jetstar will have B787's to scare off potential competitors from starting on the pacific with a more expensive type as their plans suggest they'll be competing against the low cost 787 and the Qantas A380. Also using the Jetstar B787 theory to scare Qantas crews.
Jetstar will have A320, A332 and A333.
Qantas mainline will eventually have B737, B787, B744ER and A380.