I always thought Pinsir and Jynx were a bit left out, seeing as how their counterparts got evolutions (though Jynx did get a baby like the others) but they were left untouched. I can't really imagine what Jynx would evolve into, but Jynx itself is definitely not overpowered in terms of stats or usability at the moment. It might even become a ghost/ice typing or something. Pinsir is pretty much the same when it comes to stats and movesets-- very underwhelming. At least compared to its brother's evolution, Scizor. If Pinsir got a cool evolution that was actually viable, that would be awesome.
In reality, though, I doubt they will touch anything from Gen 1. I would like to think that they do major evolution line upgrades every other Gen-- Gen 2 had a bunch of baby Pokemon and some evolutions from Gen 1, and Gen 4 added a good helping of evolutions and babies from all the previous Gens-- but for some reason I am not seeing it in Gen 6. They did literally nothing to any previous Pokemon in Gen 5, and unless the Kalos region is somehow an extension of Unova (which is geographically impossible) I don't see them building off of Gen 5 Pokemon there, either. I think Gen 1-4 were all based on Japan or areas close to it in Asia, so it sort of made sense for some evolutions to be linked I guess. I'm not sure if GameFreak actually cares about that stuff, but that's how it breaks down in my head.
I think if any Pokemon are getting new evolutions, it will be from Gen 3 and onward. I could see them sprinkling in a few more baby Pokemon here and there, like for Onix or Lickitung or whatever, just probably no evolutions. I would love for GameFreak to surprise me, though.
That was a really long post, sorry D: