one of my friend asked this question toady. if the subinterface configed with point-to-multipoint(hub) and encapsulation config without broadcast cmd. now DR\BDR election will happen ? and it need neighbor statement ??
i try this on gns3. i create a frame-realy topology with three routers hub& spoke network. on hub router created two subinterface with ospf p2m and each subinterface config without broadcast cmd. Neighbor adj don't come up
But in physical interface same config with p2m mean DR\BDR election will not happen also no need neighbor cmd.but why subinterface react different