Yeah, I like the idea, especially since a type of cabin with more capacity is easy to steal from real life, like the fold down troop seats in a military helicopter:
I'd visualize one of those carrying 50%-100% more capacity than an equivalent economy cabin, because it's just a fold down bench you're sharing with dozens of your closest friends.
I've seen it suggested elsewhere, but you could have a CG where you have to evac civilians from a station or planetary base that's currently under siege, so you either need a ship that's fast, tough, or good at silent running in order to break through the blockade, pick up your passengers, then get out the same way to take them to a safe haven. Or you could do it the opposite way, where you pick up troops at a secure base, then drop them off at a base currently under a siege. Or drop in supplies like the Berlin Airlift. Whole range of options.
See, I had thought of outfitting a Keelback as a military transport, with cabin space to fit a squad of troops to drop off and a hangar for a fighter escort. Doesn't really seem to be any missions for the role I envisage for it though.