I'm not quite sure what "sub-unbundled-FTTC" you might mean, but...
a) BT were forced to offer VULA on their fibre products, before FTTC was allowed. That's the virtual bitstream GEA service that Openreach sells to Sky etc.
b) And separately, BT have to offer physical SLU (LLU subloop unbundling) too - allowing other companies to install their own FTTC-style cabinet. Warwicknet do this, as do Callflow.