I think it more likely we'll get to the point where getting a key to unlock the bootloader requires some kind of bullshit businesses license, or else is only possible on higher end phones. Kind of like how Windows is increasingly walling options off from everyone except Enterprise users.
Or the end result of this eSIM shit comes to pass: unlocking the bootloader breaks the SIM and/or the carrier refuses to let it on the network.
But do carriers really have a horse in this race? SIMs are separately secured so all they care about is having as many in use as possible. Whatever game of cat and mouse manufacturers choose to play with the users is their business.
I don't think carriers will want the headache that comes with SIMs checking if they're used on so-and-so devices, especially if it involves depending on a service they don't control (like Google).