Having a vendor to give people an opportunity to buy the rarest if items would really help people log in, I know of 2-3 people who would play once they get an archmagi rune or whatever.
Maybe a world vendor has 2 rare runes for sell on a weekend (kind of like Xu for Destiny)
And you can buy them with tokens or blood points, or gold or whatever.
You could add a lot of different stuff in this feature and it would really trigger people to log in on the weekends to see whats for sale.
(you could even have a premade elite custom gear that is fully upgraded with a legendary and some special additional stats, and you could call it elite custom, which you could only equip x amount at a time ever. 1 weapon and 1 armor? or whatever)