Which parts of MBA-13" mid-2011 can be upgraded?
Here is what I found so far:


wifi: upgradable to 802.11 AC, with third-party QuickerTek QCard2 (manufacturer gives dimensions: V1= 18.07mm x 39.9mm, but contradicting answers on whether it's compatible with MBA2011 13"). I asked for feedback on it in a separate question; haven't tried it myself yet)