Enhancing building speed
Some benchmarks building AUR packages:
google-fonts:
darkmod:
xz could be a good compression format for server built packages, and small programs. But when the package starts to be of certain size it can dramatically slow down the building process on user machines, for very little size savings on a few packages.
This is also important because the update speed of these packages also affects the frequency which is viable to publish new updates, and with that how frequent and simple is to detect and fix new bugs.
I would build AUR packages using multi-threaded gz instead, and keep xz for the officially provided ones.