At first it didn't click me, but after I saw the Alola form of Marowak, I had a epiphany:
They are trying....to copy Monster Rancher?
From Wiki:
The characteristics of the monster (such as stats, breed and traits) are determined by various numbers stored in the game. To generate a monster, a random number generator is needed to define what characteristics the monster will have. TECMO created a CD-reading system that would use the discs to generate random number seeds and, consequently, a large variety of random monsters. The values found in the discs' data are mapped to monster characteristics.
Some discs are design to produce specific monsters, often thematically related to the disc in question. For instance, in Monster Rancher 4 the Harry Potter DVD[which?] generates a unique owl monster, and in Monster Rancher 2 and Monster Rancher 4 TECMO's Dead or Alive game creates a Pixie named Kasumi. In Monster Rancher 2, the Lost in Translation DVD generates a unique squid-like creature. Special CDs, called pandora discs, can produce multiple monsters. Often, the Monster Rancher game CD itself is a pandora disc.
The monsters in question get different kind of alternative looks or "skins" base of this factor. Here is an example of a single Monster:
http://monster-rancher.wikia.com/wiki/Category:Suezos
It is the Meta way you bring your old Pokemons into the new game.
Just think The Pokemons like the CDs you put in the game, but in reverse:
In Monster Rancher, the Monster change base the Data in CD.
In Pokemon, the Monster change base the Data in the Game.
In other words what I am trying to say is this:
In the future, when a new Pokemon game come out [Heaven & Hell?], maybe you can change the new Pokemon in Alola types, by transfer them in the game Sun & Moon.
Of course I don't know if there are similar games like these, but It seems close.

They are trying....to copy Monster Rancher?
From Wiki:
The characteristics of the monster (such as stats, breed and traits) are determined by various numbers stored in the game. To generate a monster, a random number generator is needed to define what characteristics the monster will have. TECMO created a CD-reading system that would use the discs to generate random number seeds and, consequently, a large variety of random monsters. The values found in the discs' data are mapped to monster characteristics.
Some discs are design to produce specific monsters, often thematically related to the disc in question. For instance, in Monster Rancher 4 the Harry Potter DVD[which?] generates a unique owl monster, and in Monster Rancher 2 and Monster Rancher 4 TECMO's Dead or Alive game creates a Pixie named Kasumi. In Monster Rancher 2, the Lost in Translation DVD generates a unique squid-like creature. Special CDs, called pandora discs, can produce multiple monsters. Often, the Monster Rancher game CD itself is a pandora disc.
The monsters in question get different kind of alternative looks or "skins" base of this factor. Here is an example of a single Monster:
http://monster-rancher.wikia.com/wiki/Category:Suezos
It is the Meta way you bring your old Pokemons into the new game.
Just think The Pokemons like the CDs you put in the game, but in reverse:
In Monster Rancher, the Monster change base the Data in CD.
In Pokemon, the Monster change base the Data in the Game.
In other words what I am trying to say is this:
In the future, when a new Pokemon game come out [Heaven & Hell?], maybe you can change the new Pokemon in Alola types, by transfer them in the game Sun & Moon.
Of course I don't know if there are similar games like these, but It seems close.