Well, they'd certainly have lots of Eeveelutions to choose from. Here are the ones we haven't explored yet:
Normal - surprise surprise. It never occurred to me until now that it might actually be great to have an evolution of the same type. Better stats, possibly better abilities, yeah, I can see how it might work.
Fighting - I must confess, just out of my own experience, this evolution would be the least favorite for me, but hey, I'd still use it, just for the novelty of course. I can see it being more useful in the video game though being super effective against 5 types.
Poison - Meh, we already have a grass evolution for the TCG, so since poison pokemon usually are given grass types I can't see it being all that groundbreaking. However an Eeveelution that can poison might be cool for the video game. I'd use it in a heartbeat.
Ground - Now here's a very effective possibility. In the video game, it would be super effective against 5 types, just like fighting pokemon, but in the TCG it could be helpful against Big bad electric types. Might be worth a visit.
Flying - Sure, an eeveelution that looks like a pegasus, how cool would that be? And a pain for Genesect, yep, I'd like that.
Bug - Hmmm, for the TCG maybe not such good news due to current typing which would change it to either psychic or grass which we already have, but it would be useful for the video game against overabundant grass and psychic, and the occasional dark pokemon.
Rock - Useful in both TCG and VG, yeah, a lot like ground. Can't think of even a poor excuse not to use it if it becomes available.
Ghost - Another Meh, might be ok for the VG, but typing would be redundant in the TCG.
Steel - Here's the one that would seem most logical for the TCG, but maybe not so great for the VG. In the VG there doesn't seem to be a predominant number of big bad ice and rock pokemon to contend with to see a need for that Eeveelution - but then again, that might change with a 6th generation.
My favorite hopeful Eeveelution would have to be Dragon. I think a lot of people feel the same way. It might not be great for either VG or TCG, but it would still be cool regardless, since it would be so popular.
And hey, who says that the pokemon company has to limit themselves to just revealing ... one .... new Eeveelution? Or how about maybe even some new DUAL TYPE Eeveelution? Wow, the possibilities ... Yeah, I'm really looking forward to the 6th generation games if even some of this comes to pass!