You see, whenever a Pokemon is introduced that uses an overworld item, or an inventory item to change it's forme, that item always HAS to be in the next games.
Deoxys Meteorites - They have been in every game since Gen III, as to not **** up a trainer who just got a Deoxys.
Creation Trio orbs - Dialga, Palkia and Giratina's orbs have been given in
strange plot situations or just sitting in the middle of nowherethe games that followed one way or another.
Magma stone for Heatran.
Lunar Wing for Cresselia.
hoard ofelectrical appliances.
Relic Song (Move) for Meoletta.
I'm probably missing more.
And there's no reason to think that the DNA splicers and Reveal Gas will be featured in X & Y for Black/White Kyurem and the Kami Trio respectively. And probably Mewtwo will also switch forms with some things like these.
My question being, should these items/things be used as methods of changing forms/better stats for future Pokemon?
We get ALL of these things one way or another anyway, in every game. And the list is getting bigger and bigger.