  Cerulli Irelli and Lanini have shown that PBW degenerations of flag varieties
in type A and C are actually Schubert varieties of higher rank. We introduce
Dynkin cones to parameterise specific abelianisations of classical Lie
algebras. Within this framework, we generalise their result to all
degenerations of flag varieties defined by degree vectors originating from a
Dynkin cone. This framework allows us to determine the extent to which a flag
variety can be degenerate while still naturally being a Schubert variety of the
same Lie type. Furthermore, we compute the defining relations for the
corresponding degenerate simple modules in all classical types.
