If they take the time to think up good new Pokemon (and like you said, better designs) I might be okay with new ones. I don't like 3rd and especially the 4th. xD
Maybe we'll get a mixture. A few new Pokemon and a few more evolutions. There are several Pokemon out there that need another evolution...but I'd still like some of them not to have one. :)
I liked the fourth generation. I didn't like the third generation so much. >_<