Meh. We already had full femto on a carrier network compromised. They fit in a backpack and are easy to power on batteries. And we actually use them for full MiTM. It has been done in the field. Your concerns are reasonable.

Why use an annoying SDR and a flaky LATE stack when you can just buy and root a carrier femto? :)

Also, this is why you never use your real phone at DefCon/BH... Some joker's always have these going.