I think there was perhaps a theory that LDY - MAN / BHX could benefit imaginatively from a historic route support scheme which was operated briefly in NI?
PSO is an entirely different issue. LDY - DUB had a PSO designation for a while, under a raft of such routes supported under Irish Government policy. The route to London has been similarly designated and supported as a monopoly by the U.K. Government, connecting the ‘remote’ community in the north west into the U.K. capital for key economic reasons. Having decided on that PSO it would make a return to a similar designation on LDY - DUB much less logical under the broad idea of EU PSO rules.
The idea of having PSO status applied to other less well connected cities in GB from LDY - like MAN and BHX - would simply not follow the same economic logic as supporting and preserving the ‘lifeline’ connection into London.