Personally I think it would be a ridiculous move by Seven to reinstate Today Tonight on the East Coast after 2-3 years of hibernation. Not just because I despise such "current/public affairs" programs (and yes, ACA is just as bad if not worse at times), but because the East Coast has well and truly moved on from TT by now...at least you'd like to think so anyway.
And yes, I agree with Johnston. It would be easy enough to extend the news to an hour on weeknights in Adelaide and Perth (because I'm sure those two markets currently have Seven News for an hour on weekends) and move TT to 7pm. Knowing what the ratings are like for Seven in Adelaide and especially Perth, people there would probably watch the station no matter what they put on in the early evening hours.