I suspect, when they get to redesigning the Air, that it will be slimmer and lighter and much closer to the 12" Macbook.
As long as they keep the 13" screen and reduce the bezels, the shell will shrink. The current Air was built to accommodate cooling for the Intel chips (barely). They are likely able to reduce the thickness now that Airs are fanless. Weight is likely to come down in the process.
I would expect them to keep at least 2 ports. the reason the 12" only had one was that the Intel chipset they used only had one i/o channel. Few people like the limitations of one port when data or monitor had to compete with power.