As I've played a bit more I definitely agree that it would give a very different experience, and I honestly think it would be a fun way to play through the game. One concern that I have is that of balance within those characters later on. I feel like by the time you get close to the end of a run you could become a little overpowered. One of the limits that I have encountered with normal characters is the inability to level up talents fully that are outside of your main stat, or out of your main 2. With level based talents you would be able to get the benefits from higher level str, int, and dex talents all at the same time, without encountering major downsides. I think with the mummy its fine, as the mummy has some downsides, but with the vampire it feels like it could get a little strong.
But I do think its a really interesting direction to take. Its definitely one of the better racial attributes, and as long as game balance isn't too affected I think it would be a fun way to mixup and rehash the experience. I think its taking a step in the right direction towards increased replayability, and I am excited to see how it further fleshes out during development.