The problem with the previous generation MacBook Pros aren’t that they were thin, it’s that they were thin and not built to handle being thin.
Now that MacBooks have 24 hour battery life, stay cool almost all of the time and have some of the most efficient silicon on the planet, yeah, they could probably get a little bit thinner.
The 15 inch MacBook Air is .3LB lighter than the *14* inch MacBook Pro, which is in a similar footprint to the old *13* inch MacBooks. There are some huge weight decreases that could happen along with getting thinner, as long as they don’t sacrifice the battery or performance.
Or the ports, although I wouldn’t be shocked to see them drop the HDMI for another thunderbolt port and just keep the SD card slot.