While I like options, I personally think that'd be unnecessary. Typically if a player is using drag-n-drop, it's because they know what's in that city and just want to rapidly move it. If they have say, tanks, infantry, and bombers on a city and only wanna move the bombers, they'd simply click that city, click 'move units', select the bombers, and move them. And then once those units are seperate, they can drag-n-drop.
All that needs to be done is make it so militia aren't included unless you're using gurellia warfare. Without that strategy there's no reason to move militia for the most part, so when a player uses drag-n-drop, they don't want the militia included.
Also, if you think about it, how would they adjust what units are drag-n-dropped? Would they have to change their settings every time they wanted to take different units? Make it so they only drag infantry and tanks, well what if they wanted to throw in some bombers and unique units, would they then have to go and change their settings to include those units?
In the end, simply making it so militia aren't included would suffice, after all that's how it use to be and nobody cared. If it aint broke, don't fix it.... even if it is currently broke.... <.>