I don't know. I suppose it depends if PSO routes can have codeshares on them.
Yes, they can.
Article 15(4) of the Regulation allows operation under code-share agreements and does not exclude the case of PSOs, so such agreements are in principle admissible.
As the WG says there will be no further subsidy other than a 'modest marketing budget', to me it all points to a way of helping Flybe grow its CWL operation. The WG believes the lack of APD and exclusivity on a route for four years would entice airlines to operate a thin route that was previously not viable. Would the WG want another airline or airlines to step on Flybe's toes which could be the case with restricted (exclusive) PSO routes which is the type of route the WG is looking at?
If another airline - say bmi regional or Eastern - won the PSO contract for a route or routes they would have the expense of setting up a base without, it is said, any help other than modest marketing from the WG. We know that the WG and Flybe already have a major relationship with substantial financial input from the WG, so a Flybe-operated PSO route or routes probably would not entail any further subsidy as it would doubtless come out of the agreement already in place. So it seems likely that Flybe would be the winner if several airlines put in tenders.
A few more points from the EU Interpretation of PSO routes:
A 'double drop' PSO route must qualify on its own merits for PSO status.
While PSOs could be designed to lift hurdles to the economic and social development of regions or cities, they cannot be established with the aim, directly or indirectly, to promote or support a particular air carrier or to develop a particular airport.
Where train services serve a route at sufficient frequency and with a travel time of less than three hours PSOs should not in principle be imposed on air services. However, there can be an exception if the train route does not offer adequate connectivity to medium and long haul air routes.
If routes from nearby airports are already available a PSO would require a 'particularly robust' justification. If another airport is farther away than 100 km and/or the travelling time is more than one hour by public transport, it is generally reasonable to question whether the two airports can be seen as alternatives.