Giratina speculation
For the last month, we've been doing Giratina's Altered forme as the tier 5 raid. People have wondered where the Origin forme is.
I speculate that we won't have a separate set of raids for the Origin forme, but rather that we'll have an object that we use on an Altered forme to turn it into an Origin forme. Not sure where or when this will happen, but that's my guess. It could also be that Origin forme comes later. Finally, I speculate that Origin forme might have better moves (Shadow Ball, Outrage, etc.)
We'll see, eventually.
Answers
As important as forme changes are to some pokemon, at this point I am expecting Niantic to just take the lazy route and release all forme changing pokemon as separate pokemon.
That is what they did with Castform, despite dynamically changing forms being as important to it as transforming is to Ditto.
They couldn't figure out a way to implement Shedinja's evolution or ability.
Any pokemon that deviates from the regular format, I am no longer expecting them to bother to do anything special with.
Echoing the above sentiments, Niantic doesn't seem too keen on implementing the ability to change formes any time soon. Castform's stuck with whatever you catch it as, Deoxys's formes seem to all be separate entities, it looks like Giratina will be handled the same way.
I really, really hope the charge moves coded for Giratina-O are just placeholder right now. My boi deserves better than Shadow Sneak.