The biggest threat to Bitcoin isn't Blockstream or another coin replacing it but a central bank digital coin which will have all the convenience of crypto without the decentralization.

It'll let its users enjoy scaling and security without decentralization or privacy (from the issuing bank). The only challenge the banks will have to solve to replace M1 with CBDC is finding a way to monitor tx's and prevent unauthorized exchanges with decentralized crypto not under the banks' control.