One monohead to rule them all. Same heavy duty form factor with the pro-quality back handle, knob, and stand spigot. 1000 w/s, and can be used with either a high capacity battery, or true AC power. All flash specs equal to or better than the current B1X or D2. This would be THE light for me.
A dummy battery that can connect to an AC adapter so the A2 can run on AC power. I like this idea since the A2 cannot run on AC as it is. I often use my B10s and A2 as a trio. When setting up a studio on location, it would be great to be able to plug in if I choose with the A2 as well. I run the B10s on power all the time. I love being wireless... but sometimes it's handy to be able to plug in and save the battery for later.