One of the advantages given for STOVL was the ease of conversion for RAF pilots to operate from the CVF and the limited currency training needed. The CTOL version will need a longer training period and very regular currency training. I am not sure it would even be possible taking into account the periods where either the CVF or RAF squadrons would not be within range due to detatchments/deployment.
It would raise the issue of the viability of the whole JFH concept.