This thread is a really cool idea, and I've enjoyed participating in it and also enjoyed reading it a lot.
That said, I know for me personally the high cost of postage makes it a bit suboptimal.
It seems a bit inefficient to spend $4 to send someone a $6 tin of tobacco.
I have done a LOT of trading and swapping of cigars, but there the numbers make more sense, I think, because it's super easy to break open up a box of cigars and send a few to someone and your average cigar runs $3-$5 each so a five stick trade is $20-$30 in cigars, if not $50 in cigars, and then spending $4 to ship it is pretty easy to justify.
I've been brewing a thought for a while though about doing some sort of group buy box pass pipe tobacco thing. First, figure out how many 2 oz tins fit in a small flat rate box (I think $9 to ship) and then have a bunch of folks all send $ maybe a tin or two worth of money and group it together, make one big purchase of tins from one of the vendors that offers flat rate shipping, and then have each person receive the box, bag up their own 3 or 4 gram samples, hell maybe even put a scale in there, I dunno, and then send it on. Everyone would pay the same $ for tobacco and pay one fee to ship the box down the line. You might get to try 15 different kinds of tobacco for an investment of $20 or something like that.
This idea might not be totally workable, but it strikes me as the general type of idea that might really work as something that is hard for us to do individually (try a bunch of tobaccos in an economical way) but might be easy to do collectively.