Is traditional cash really a problem? What problems does cash solve that pucca shells do not?Seriously? The advantages are legion. It would take days to write them all out. I'll just put down a couple. You don't have multiple denominations of shells, so you have to carry around a wagon full of shells, instead of a few large bills.
From a macro perspective, cash has even larger advantages. You can't conduct monetary policy as easily with a commodity currency. One reason recessions were so bad in the past (in the 1800s) is that commodity currencies are pro-cyclical, partially because of nominal stickiness, partially because of speculative attacks, and for other reasons, too.
For me, what's the advantage of replacing my credit card with a phone? My wallet becomes 1mm less thick, unless I want to carry my credit card around as a backup in case my phone battery dies. In a few years, when this becomes standard, and phones are good for multiple days, I'll be able to shave 1mm off my wallet. That's nice, but hardly analogous to the difference between paper fiat money and a hard commodity currency.