Make it lighter and thicker.
Seriously, until it's as light as a phone I don't mind if they keep shaving weight off. But there's very little to be gained by going thinner:
1. I doubt ergonomics get much better as it approaches typing on a sheet of paper
2. the risk of bending increases
3. if it's not as thin they can fit more stuff in there more cheaply: better heat management, longer lasting batteries, faster processors/more memory, stronger antennas, etc.