Yeah, we're a little off-topic...but while we're here
I've been making separate-piece bottoms. It looks good and it's pretty easy if you pin it first and account for a bunch of little darts. If you don't, it's a PITA - BD can attest to that!
I like the folded idea, but like I said, it seems like a lot of wasted material. Although it's only sil so it's not like it could weigh much.
My sack idea would have two chambers, end-to-end like you mentioned. However, the two drawstrings would be on each end, not one in the middle. The middle would be a separate-piece sack bottom type partition, with a hole like in the end of a 'blackbishop sack'. Think of a normal 'blackbishop sack', but with another sack attached to the end so they share the bottom.