The NPPL was NOT designed for 'medical conditions' - it was designed to meet the requirements which industry had said they wanted. One of which was that 'The course shall be undertaken at a UK flying club/school or flying training organisation'.
The next ANO amendment will introduce changes which will be of considerable benefit for those wanting to fly SSEA, Microlight and SLMG aircraft without the need to revalidate all classes independently - and it will also get rid of the 'rolling validity' concept.
As for statistsics - nope, I don't have any.