If the current shenanighans with Glasgow's attempt to get to grips with their new electronic filing, and the proposals of EASA for mandatory written flight plans even for class D transits bear fruit (consultations now closed apparently) then we are all going to be filing friggin plans whether we like it or not. Alternatively opportunistic transits of class D will simply cease, and access to huge swathes of CAS will no longer be available to VFR bimblers.