Why can't ecash be for payments? I personally wouldn't want large amounts of long-lived amounts stored in a fedimint. The former reducing overall rug risk and the latter reduces the chance of inflationary practices (aside from running a client that validates the version of fedimint run by guardians).

Fedimint doesn't explicitly have to be a "bank", although, admittedly, that's been a advertised use case from louder voices than mine own.

Laying out an example:
I'm visiting LA. I somewhat know people in the area, maybe I'm visiting them. There's a smaller network of merchants that participate in a fedimint. Similar to handling cash, they don't keep large amounts in the drawer (in the fedimint). Just enough to do business of the day. When i arrive, I can peg-in (on-chain or with LN) to the fedimint and now have ecash to spend. Each merchant and myself don't have to mange LN nodes and the complexity inherent to it.

Another:
Remove the ecash/BTC/LN modules and insert a password manger or any other arbitrary data. Since the data is validated via consensus among fedimint nodes, the risk and access is distributed. It enables the syncing and validity across disaggregate nodes. 

I personally would love to auto-sync my bitwarden instance between home and office servers. I understand there are solutions to that with some automation, but fedimint could offer this out of the box for the less technically inclined.

Myriad of solutions and fedimint could be one. Definitely not the end all be all, but i have to pick something to focus on with my limited time. 🫠