Ah, I see.
I'm still going to give this a serious response, though, if that's okay.
Basically, this is a different situation than Nintendo software on Sony or Microsoft hardware because there are no compromises necessary when going from lower spec to higher spec. Killzone on the 3DS, though? You know as well as I do that it would be a serious downgrade from Mercenaries. Also, my apologies, but I'm in love with the Vita hardware, it really is a lot better than the 3DS hardware, and I'm not saying that to offend anyone or make some kind of fanboy stand--that's just how I honestly feel.
Quite honestly, though, aside from Sony's excellent LBP Vita game, there isn't a lot of value in their portable development franchises, though the games they've made in partnerships, like Soul Sacrifice, would probably do quite well on the 3DS.
Sony banked on the Vita hardware selling itself, like Nintendo did with the Wii U hardware, with the games as something of an afterthought, and both paid the price.
Personally, I'm not exactly opposed to Sony developing games for the 3DS, I just don't want to lose my lovely Vita. If the 3DS hardware was better, though, then that would be kind of awesome. It would be even better if Nintendo and Sony could partner for a P-DS device. That would be a monster.
