I'd like to see a way to post artifacts for sale to other players. Restrict it to artifacts that can normally be traded, even limit to one's legion if need be. I think it would be great though, because people are already doing this, but the means by which they have to do it is really clunky and awkward.

i would agree with this in many ways

the way I see this working is there is a trading market tab where the artifacts are sorted into what kind they are
buffs
traps
planetary
etc
etc
then it's sorted into who is buying or selling them and what their prices for selling are and how much they are willing to buy them for.

example:
Trading Market
Traps: Planetary Ship
Planetary: Offensive Defensive
Ship Buffers
Ship Nullifiers (Emp sphere, etc, etc)
Miscellaneous (Time Manipulators, Probes, Repair Drones, etc, etc)
and after you click on what group of artifacts you're wanting, you'll see who is selling them
for example

Miscellaneous:
Kalos - Repair Nanodrones - 10 for 1,000,000,000

that's the kind of way I see this working.