It's a little dickish. That said, I don't think it's unethical. Ex-employees writing 2.0 happens all the time. It usually doesn't work, but it can. You may, h

It's a little dickish. That said, I don't think it's unethical. Ex-employees writing 2.0 happens all the time. It usually doesn't work, but it can. You may, however, run into issues regarding IP even if you do a re-write. IP can cover more than just code.