Highly unlikely for any side to launch a Tet style attack.

For the following reasons:

1. All sides are to fractious to coordinate such an attack, not exactly a central command coordinating all insurgent groups not like the Vietcong and the NVA during the Vietnam war.

2. No cooperation between the potential insurgents namely the Shias and the Sunnis. The Sunnis are now begging for U.S. help vs. Shia militias and death squads.

3. If there were a Tet style attack, the Shias probably has the best(still remote chance) of doing it but it will be confined to Shia dominated areas such as Basra and parts of Baghdad. The Mahdi militia tried an uprising a few years back and got its ass kicked.