Get your nuln oil ready? I'd honestly rather get my 'empire-infantry-aren't-shit' oil ready!
The empire gunline is fine. One of the better empire lists, actually. And we can already make a good mounted list, so we don't need a new mounted specific army of infamy IMO.
Let's assume we get a Nuln based one. Fine. Our best bet for the other is a Middenland/Middenheim focused one, in my opinion.
In the old Storm of Chaos campaign in the early 2000's, the middenland list had infantry that were better fighters/cheaoer, but lost the detachment rule. As the detachment rule is straight garbage, this would be a complete positive.
I'd be happy to see the war wagons come back (maybe as a lower tech middenland alternative to the steam tank?), and the old (4th/5th edition) empire character on pegasus.
http://www.sodemons.com/rhmarauder/mb15pegasus/index.htm That pegasus looked a lot more awesome than the gelt pegasus.
The thing I'm looking forward to most with our arcane journal is actually getting play an empire army with...empire army special rules. Our current army, alone out of all armies, has none, which is probably why it feels so bland to play.
At my most recent tournament dwarf players outnumbered empire players 3:1, even though I think the empire tournament level lists are slightly better.
My secret wish : we get three armies of infamy, one for each of the three emperors.