The fedimint custodians cannot unilaterally rug you, but they CAN arbitrarily inflate the token supply unless the tokens have some kind of cryptographic claim on the sats held by the mint. When a fedimint becomes popular, there is no way to audit the issued tokens unless privacy is eliminated. The technology for cryptographic claims on lightning sats is imminent, and possible, just not designed yet. If it becomes feasible, the cashu mint model will provide sufficient guarantees of custody, relying on the lightning network enforcement mechanism, and a fedimint will be unnecessary and likely cumbersome.