>dedicated 22LR upper
>22LR conversion BCG
For survival stuff, honestly, I would either forgo the BCG and have a Ruger MKwhatever, or have a 22LR rifle. The pistol will be about the size and weight of the BCG kit with 22 magazines, yet be more reliable, more accurate (with a steady hand), and will keep the rifle in good clean shape when 223 medicine is required. If you can spare more than that, such as an upper, or if you think you'll need more than 22LR pistol practical accuracy, jump straight to a Marlin 795 or 70PSS or 10/22 Takedown. Although I lean to the Marlin rifles for various reasons, a comparable 22 rifle will be close in size/weight to the upper, and be very practical for all situations in need of 22LR when a pistol wouldn't be as effective.
I'd rather have a Ruger MKwhatever and zip-tie some pool flotation foam to it. It'll be more accurate, more reliable, more durable, smaller, and lighter overall. The AR7 to my mind was a decent idea, but so poorly executed that it is mostly self-defeating. Marlin and Ruger takedown models perform brilliantly and do what the AR7 wanted to do without being that much heavier or bulkier. Remember that although the AR7 sounds compact, when you hold one, it really ends up being like a fucking Michelin-Man rifle; puffed out and comically lumpy from having to stuff itself in its own stock.
Then there's the Browning carbine things. I've always wondered if one could be offered with a removable stock setup to basically do an effective pistol-becomes-rifle job. I know that putting a stock on a pistol in the USA is a legal problem, but with paperwork or if we are in a survival situation, this issue could be irrelevant.