https://www.klemchuk.com/ideate/encryption-backdoors-and-bal...
Pubicly proposed interception mechanisms, like the Clipper Chip, were widely referred to as a backdoor, as have those put forth by the UK government recently for encrypted messaging apps
https://www.express.co.uk/life-style/science-technology/1556...
>>backdoors are defined in part by whether or not they're expected and wanted by the end-user,
This would not be wanted by the end-user. The backdoor in this case is just an imposition on the receiving party, i.e. the merchant, that they'd rather do without.
No tool to let the state eavesdrop on or surveil one's private affairs is wanted by the party being subjected to it. This is unequivocally a backdoor, and it would only win out in the market if tools without backdoors are eliminated from the market by the state, using the state's apparatus of violence (the police, courts and prisons that gain compliance with government edicts).