I tried to describe a dual currency model, in which a fungible hard currency (monero) facilitates the productive functions of capital markets, and an inflationary or freigeld-class of currency floats against the hard money, at some market value. It is the issuance and distribution of the latter which provides UBI. But in order for capitalists to sell their goods, they need to accept and exchange freigeld.
Remember Gresham's law. The currency undergoing inflation or demurrage will see transactional demand, while the hard money will see reserve demand. The clearing exchange price will depend on where the ISLM curves of the two currencies balance.
This is why I was pushing for Monero to have an exponentially increasing money supply in our old economics thread debates. An electronic cash with a higher transactional demand can penetrate markets much faster (assumption) because even the earliest of adopters have incentives to spend it. I believe this is at least partly why Bitcoin hasn't exploded into popularity as quickly as many expected. What is the ratio of people spending compared to those waiting around for the price to go up?
I don't think a single money can serve as the preferred currency for both transactional and reserve purposes.