eCash is offline capability. It's just a string of data with a client that knows the pubkey of the mint to verify the signature on the eCash is valid.

LN, you have to manage liquidity. eCash on Fedimint, you do not. FM has LN Gateways which are LN node that have their own operators and mange their own liquidity. Similarly, Guardians are already trusted to manage your "system". I would expect similar relationships with LN Gateways.