To be honest, I doubt many ISPs would consider it worthwhile given the limited size of the market. There's also the disproportionate cost of structuring Kingston services along wholesale lines like BT has had to do. It costs a lot of money to develop all the systems and mechanisms to present such services, along with all the structural re-organisations involved. BT can spread the cost over a huge infrastructure and revenue base, whilst Kingston have a much smaller one.
From the SPs point of view, it's yet another systems integration job with all the automated and manual interfaces, configuration management, problem management and much else. We already see this with the limited support for Openreach's GEA-FTTP services, despite them being close cousins to the FTTC ones. All this costs money for ISPs.
Incidentally, this is also an issue for altnets in receipt of public money (like Cotswold Broadband) , where open, wholesale service is mandated. Just how many ISPs will think it worthwhile to provide a retail service for a few thousand potential customers?