Well it's all a bit vague in my mind, but the idea was that if a central bank coin is introduced, and if it achieves widespread use and popularity such that it becomes the default demand deposit mechanism, that the central bank could purchase the dispute resolution units from the private banks that presumably no longer have a use for them. The systems and human capital expertise to perform the functions would still exist, but it would be a question of whether they would be willing to work in the public sector instead of the private, and if the public sector could effectively manage them such that their performance remains acceptable.

From the description it sounds as if charge backs would be entirely possible given the suggested centralization aspect of the coin. Dispute resolution is relatively simple solution, especially as many banks will no longer require that sort of service.