Exeter is a whole bag of spanners just by itself!
They have tried to do something which is probably a good idea. However, the wording used in the AIP and elsewhere to acheive that objective is wrong.
There is no such thing as an "unmarked displaced threshold". When displaced, the displacement has to be visible to aircraft on approach.
Taking the 08 Exeter example, they are trying to do what many aerodromes in Europe and elsewhere do. They want single engine piston aircraft who do not need the full runway to touchdown well after the threshold. This places them higher over the obstacles prior to the threshold than would be the case if they used the standard aiming point and approach angle.
Unfortunately, every other aerodrome that uses this procedure specifies the "touchdown point" / "aiming point" for single engine piston aircraft. The threshold remains in the same place but the distance from the threshold to the SEP aiming point is greather than the distance to the standard marked aiming point.
ILS and PAPI can only be used when the standard threshold and aiming point are available because this is where they are taking the aircraft to.
Since SEP on 08 at Exeter are using a different aiming point then while making a 3deg approach to that point they would always be above the slope indicated by the ILS / PAPI. Or looking at another way, following the ILS / PAPI would take them too low on the approach and defeat the whole objective of having the separate aiming point.
Having said all that - landing well beyond the threshold is totally different from landing before it and brings up a whole different set of issues.
Regards,
DFC