BLW,
You are one of the people the NPPL will be attractive to however, the swap over to a JAA PPL will not exempt you from anything that you would have to do if you went straight to a JAA PPL.
The nonsense is that you could be quite competently flying your SEP with up to 3 passengers on a NPPL but, have to do X hours DUAL with a FI before you could be deemed safe to fly the same aeroplane with a JAA licence. Nutts! isn't it. And some say it has reduced beaurocracy!