As long as it's optional and they still allow BYOD it's a good solution for some customers.

BYOD barely existed for cable (since DOCSIS specifies ISP remote management as part of the spec) and doesn’t exist at all for fiber. If you mean your own router: yeah, I do that, they don’t support it but there’s no real way to stop me? I do end up double-NAT’d but my real router is DMZ’d so there’s no practical issue… until they start issuing IPv6.