Notes on sub-dexes.

Kalos:

Central Kalos: 153(Starters and Mythicals)
Coastal Kalos: 153(Fossils and Legendary Birds)
Mountain Kalos. 151(Pseudos and Mascot Legends and Mewtwo)

Alola:

Full Dex: 301
Melemele Dex: 120(Starters and Tapu Koko)
Akala Dex: 130(Fossils and Tapu Lele)
Ula'ula Dex: 130(Ice-types and Tapu Bulu)
Poni Dex: 100(Pseudos and Tapu Fini)

The future seem to look something like this:

1. Gen 8: Five subdexes with recurring species. 107 species per dex at maximum. Total around 450.
2. Gen 9: Six subdexes with recurring species. 84 species per dex at maximum.Total around 350.
3. Gen 10: Seven subdexes with non-recurring species. 61 species per dex at maximum. Total around 420.
4. Gen 11: Eight subdexes with non-recurring species. 50 species per dex at maximum. Total around 400.
5. Gen 12 onwards: Subdex count increases with per dex count remains similar. Subdexes would instead have their own subdexes from now on, like cities, towns, prefectures etc.

Some alternative ideas would be:

1. Each subdex can get its own starter and sub-legendaries, with final one having the mascot legendaries.
2. Each subdex can have its own early game stuff.
3. Each subdex can have the same dex structure with same primary or secondary types and similar stats, but with different species. So for example, 147-150 would be Dragon pseudos,  015-018 would be early Flying-types, etc.
4. Each subdex would be divided in terms of BSTs, with lower BSTs belonging to earlier dexes and so on.