Someone needs to make a sticky topic on the specs of a 3DS. the 3DS is not capable of rewriting the data of a physical game cartridge. it WOULD be possible for digital only copies of games, absolutely, it would be just like an app on a smartphone or tablet where the overall program is replaced by the new one (basically) but the 3DS does not have the ability to rewrite data on a physical game card.
The patches and corrections that have been released are to fix programming errors within the 3Ds or how the 3Ds interprets data from the game or online. They can't add whole data into the game in the form of new pokemon, items, and so forth.
Now, the fact that Torchic with it's Blazikenite being available from day one should be a very clear indication that the data for all the items and mega evolutions is ALREADY in teh game data. (Since it was given out to everyone with either game, there was no need to go through the data to look for where the Blazikenite was stored and Hello? Mega Latios and Latias? :-) ) Just because the hackers haven't found the location of all the data doesn't mean it's not there. Look how many months it took for them to discover the shiny forms of Xernes, Yveltal and Zygarde. If it was that easy to get all the data, they would have released the shiny forms at the same time they discovered Diancie, Volcanion and Hoopa.
You make the claim:
"when a new game came out in the same generation with a new form, users of the older games would not be able to use (or even see in battle) these new pokemon."
but what EXACTLY are you referring to? The only pokemon I am aware of (and I did skip gens 4 and 5 so there are easily tons I don't know about) are Deoxys from gen 3, and that wasn't a matter of older games not being able to use/see them as much as version exclusive forms of Deoxys being in play. (Ruby/Sapphire got normal form and that's all you could see when battling, Fire Red got (i think) attack form and that's all you could see when battling, LEaf Green got (i think) Defenses form and that's all you could see when battling and Emerald got speed form and that's all you could see when battling. Fire Red and Leaf green came out at the same time and Emeral came out after all of them, so it was obviously a concious decision by the programmers to only show that form in each game for whatever reason. It wasn't until gen 4 that you could have multiple forms in the same game. And the other being Kyurem, but again, that seems to be simply a matter of the item needed for transformation being in a later game and, more importantly, an additional reason to buy two more of the games you already own! ;-) But other than those two pokemon, I have absolutely no recollection of any pokemon (in the same gen) being barred from going back to the old game. Technically Kyruem Black and White can't even go to a future game without first being diffused into it's two composite forms
