Well, I’ve always liked the idea of setting a game in the past; I think I’ve talked about it before.  I don’t think I see how reviving Pokémon from fossils would fit with that theme, though, since the games have always presented that as a very recent development made possible through modern technology.  The idea of setting a Pokémon game in an older version of the world, with a very different social structure, is certainly a big draw; in particular, if you’re working in a period where Pokéballs are a rare curiosity created exclusively by elite artisans, we’re bound to get a very different view of the relationship between humans and Pokémon than what we normally see – or, alternatively, a strikingly similar view that could say some interesting things about how that ideology developed.

Other than that, I think the main attraction of the idea for me is in working out replacements for a lot of the conventional systems that sustain the Pokémon world as we know it – there are no Pokéballs, so everyone has to rely on apricorns; there are probably not a lot of standardised items like potions and revives, so everyone has to use herbal medicine; there’s no PC network, so everyone has to store Pokémon in actual physical locations like farms; there’s no remote communication, so people in other towns have to be contacted by messenger or telepathic Pokémon.  The danger is that, in the process of working out all these ‘immersive’ systems, you inadvertently create something that’s just full of annoying chores – things like growing apricorns and preparing herbal medicine have to be parts of the game in themselves, things that can be fun to do and have potential for major rewards, and there need to be as many ‘convenient’ options as can be justified.  I’ve often toyed with the idea of a system where you can cross-breed apricorns, gradually gaining access to more and more useful strains that create Pokéballs with all kinds of fun effects – start with just Pale Apricorns, which just work like regular Pokéballs, then find each of the seven standard apricorn colours (blue, red, yellow, green, pink, black and white) and start crossing them together to create things like a Sky Blue Apricorn that’s especially effective against Flying and Levitating Pokémon, or a Deep Violet Apricorn that increases the experience growth of a Pokémon captured in it.  Basically, make the players work harder for stuff, but be sure to reward them for it!