It doesn't need a softfork - only if we absolutely need the ability to receive transactions when offline.
Ark requires BIP-118 or BIP-119 covenant primitives to constrain transaction outputs of a spending transaction to make the receiving on the protocol non-interactive. BIP-118 ANYPREVOUTANYSCRIPT can constrain the spending transaction by hardcoding a 65-byte signature and a 33-byte unknown public key type in a script. Alternatively, BIP-119 CTV can directly constrain transaction outputs to a template hash. Other alternatives would be (1) TXHASH, (2) CAT + CSFS + TAGGEDHASH, or (3) XOR + CSFS + TAGGEDHASH combinations.
These covenant primitives can be emulated using n-of-n multisig by compromising on non-interactivity. Recipients must be online to sign from the n-of-n multisig to constrain the spending transaction. This interactive version doesn't require any changes to Bitcoin and, thus, something that can be deployed on Bitcoin today.
needs a softfork
We are better off building a completely off-chain system, using a normal database to keep track of BTC transactions. Reserves can be audited on mainchain at will. Sure you are going to have bank runs and it sucks. But thats just part of life. ACCEPT IT