There is talk on Nintendo on possible type changing to any pokemon through chromosomes. GOD PLEASE DON'T NINTENDO!
Changing any pokemon's type to any other type? No thanks.
Modifying a pokemon's type to a select few other choices? Maybe. (big maybe).
A pokemon's typing is one of the biggest things that define them, so messing with that could make everything a bit mushy (for lack of a better word).
I would like to see a new type, I've wanted to see a new one for a while. Light/Celestial/Genetic, are all decent options (I can't really think of anything else), and I'd say Gen VI has a good opportunity to implement it, especially looking at the legendaries with dubious characteristics.
However before we add a new type to the mix, old types need to be fixed up.
-Ice needs actual resistances, and a stronger benefit from Hail.
-Poison is pretty much a lost cause offensively, but defensively it could really use some new moves. Toxic/Tox Spikes are generally the only poison type moves you see, (other than a couple fishing for an extra stab, like venusaur or nidoking) which is disappointing. I think a unique leeching effect could do them good such as,
75 base power, restores 1/4 hp of damage dealt, boosts defense or spD by 1 stage. Something along those lines.
-Ghost and Dark both need better stab options than Shadow Ball and Crunch which have been around since gen 1 and 2 respectively, it is time for an upgrade.
-Rock needs a 100% acc move.
-Flying has gotten to the point where it has a good selection of moves (Brave Bird, Hurricane, Air Slash, Acrobatics.... yet there are still so many flying types that lack a proper STAB. Again, really disappointing.
-Some higher distribution of certain unique moves to other types would be nice, such as U-Turn clones, priority move clones, or recover clones (roost was a good start, how bout Cauterize for fire types, Hibernation for ice types, Rebuild for rock types, etc)