If there is to be a PSO on LON-NQY I would imagine:
- It will be optimised for travellers from the NQY catchment travelling to London
- It will focus on point-to-point rather than connecting traffic
- It will be agnostic or largely agnostic in terms of London airports (because the goal is to link Newquay to London, not to a specific London airport)
Of course everything depends on the number of seats specified in the PSO but would there really be more than e.g. 50 people travelling by air from NQY to London on a typical morning?
This suggests to me that the most likely scenario is something like an ATR overnighting at NQY, flying up to LTN/STN/SEN in the morning, and then either doing other things out of London during the day (unless it's an old enough and cheap enough aircraft to be parked all day) and then returning to NQY in the evening. (I include SEN because Aer Arann has plenty of PSO experience and might fancy being indirectly subsidised to fly a couple of daytime routes out of SEN.)