I believe 201+ because in Gen I, we had 151 Pokémon; Gen II, we had 251 Pokémon; Gen III, we had 386 Pokémon; Gen IV, we had 493 Pokémon. So assuming in Gen V, we will have over 201 Pokémon to equil almost 600+ Pokémon.
I remember in Gen IV in D/P/PL at Dawn's House, the guy sitting in the chair said that we had almost over 500+ Pokémon. So I think that their will be 201+ more Pokémon.