I'm going to make a Pokémon T-Shirt series and I asked myself: "What do the Pokémon fans want from a Pokémon T-Shirt?". So waht do you want from an inspired Pokémon T-Shirt? What styles do you prefer, what subject do you prefer? What color do you prefer? I'll consider all of your suggestion and I'll keep you informed about the developing of them.
Hm, I was contemplating whether or not this was relevant to A&D, but honestly, it sounds to me like you're looking for inspiration and opinion on what direction you should go with a piece (granted, a different medium). As long as you're not trying to sell your shirts here, I think there's a lot of potential for discussion in this.
Personally, I would want a shirt that represents the things I like about Pokemon as a 22 year old girl, but that may not be in demand. The kind of Pokemon you choose should depend on your customer basis.. but I think there's a lot of room for grungy Pokemon art out there. I would want something that captures the competitive edge of certain Pokemon, and showcases their skills beyond what the anime displays.
I hope all of that makes sense! If you can tell us a list of Pokemon you're considering, maybe we can help you come up with good backgrounds and appropriate text for them? Keeping in mind what would look good for a t-shirt as opposed to paper makes for very interesting conclusions, in my opinion.