There may well be good reason, but I am still trying to figure out how non-interest bearing cash is likely to fit into a broader bond market system.
For non-interest cash to find use in transactions, it would be important that it not get hoarded at fixed terms in the bond market to earn a yield. This hit me (*) in a recent discussion about 14% yields on roubles. Particularly when interest rates are high, I think this would require an interest-bearing at-call deposit market so that cash is able to move freely rather than be locked up. (*Till then I too thought that you might get away with just cash and term-based lending.)
One possible advantage of having cash in addition to at-call deposits could be that the at-call deposit market could be set up as block-chain based accounts that allow negative interest rates on the notional cash within it, when this is necessary in certain cycles to balance supply and demand. See The Zero Interest Bound Problem here...
https://bitsharestalk.org/index.php/topic,15880.msg203780.html#msg203780However, it may not be necessary to have a separate cash market to accommodate this – the cash units could be purely notional and only ever exist inside the accounts if there is some type of check-based system to move those notional credits. And allowing exchange above the feed price is an alternate market clearing solution to allowing negative interest rates. In other words, you could conceivable do away with cash and just have an at-call deposit market.
It is possible there are other reasons why users may choose at times to prefer to have a separate token for non-interest cash compared to just "interest bearing deposits". I feel these reasons need to be clear to justify the existence of a separate cash market. Possibilities might include increased privacy or anonymity, increased security/collateralization, or the ability to offer some cash-based services without the complication of dealing with interest payments on behalf of clients. Or I suppose we could just build both a cash and at-call deposit market and see how people use it, but as per my initial point, I don't think cash negates the need for an at-call market with interest.
Any thoughts?