SR can provide RPM WAP 7 anytime to any train, it is not necessary that the train should be Mail or Superfast.
If you notice WAP 7 is sometime used to haul Coimbatore-Nagercoil Passenger only from Erode to Coimbatore.
Raptisagar also once got WAP 7 from Chennai to TVC.
WAP 7 will be given only once the full route is 100% electrified and all...
more... the Sub Stations working.
Coimbatore-Mangaolore Intercity will get WAP 4 mostly but there are chances of it getting P7.
12685/12686 will also get P7 but only in June or July.
RPM have more than 50 P7, some P7 are used to haul Passenger trains in Karnataka.