I've been wrestling around with the same.. a backpack'able AR.. but the more I look at it the less I like the AR platform and 556 for that purpose.
My 10.5" is a great "truck gun" kept whole, or even with its pins pulled.. but carbine length gas is as short as I'll go. The muzzle blast from a 5.56 is just barely tolerable at 10" with ears on, 10" or less would be absolutely deafening if used without ears in a self-defense situation, worse yet.. deaf for days if it happens indoors.
While I really like the idea of a mini-AR, the compromises and realities aren't a good fit for me, so I'm looking at options such as the Ruger PC Charger, Sig MPX, etc, etc...
Also, in a hotel with people in every possible direction except out the window... I'm thinking one of those shorty shotgun things with turkey loads might be best lol.