As already said, you can buy another cloak for 10k-discount.
But when you look closely, you will find that the legendary cloaks are not unique like their epic counterparts:
Xing-Ho, Breath of Yu'lon.
So this could mean there was a datamining bug, it was forgotten by Blizzard, or that we can have at least one epic cloak additional to the legendary cloak (when the augmentation is a one-time quest), or that we can have several legendary cloaks when you can repeat the augmentation.
The latter two possibilities fit Ghostcrawlers announcement:
https://twitter.com/Ghostcrawler/sta...29202236579840