The problem about not keeping the interest on the float is, who do you pay it to otherwise? If you have a truly anonymous digital cash system, you couldn't find the original purchaser if you tried. If you want to treat this like a settlement problem in securities operations then you have to track each owner's interest share for the time they held the instrument and pay them back. Again impossible. If you pay back the accrued interest on that specific ecash certificate to the person who "walks in the door" with it, is it fair?
Fair? Who cares? The question is, is it useful? Sure it is. I'd rather use cash which bore interest than that which didn't! Sure, it's a little more complicated to buy something with notes which are worth $1.05 - $1.10 than $1.00, but that's what computers are for. The value increase accrues to whomever holds the note during the time they hold it.
I don't see where this complication arises from. Assuming that you have already created a floating rate exchange apparatus between dollars and digicash [maybe you aren't making this assumption and that is where my confusion arises from] all you have to do is invest the money that backs the digicash and make regular, frequent and public reports about how well it is doing. The exchange rate will then naturally parallel and the interest problem is solved without any extra more complication than is involved in the creation of a floating rate exchange mechanism. JWS