The study of the treatise is ongoing, and discoveries continue to be made. For instance, in the mid-20th century a copy of it (with some variations) was discovered and recorded in Beirut, Lebanon, at the end of a series of inscribed plates that record the Book of Ezekiel.Before this, the most recent information was that these plaques had been removed from the (traditional) Tomb of Ezekiel in Iraq over a century ago. I would be interested in hearing more about this recent research that suggests otherwise.
Those plates are now at the Yad Ben Zvi Institute in Israel, although the plates containing the treatise itself are now missing. Recent research has revealed, however, these plates were created in Syria at the turn of the 20th century, about 100 years ago, suggesting the treatise was being told in an elaborate way up until relatively modern times.
I have recently published the first complete English translation of The Treatise of the Vessels (Massekhet Kelim) in Old Testament Pseudepigrapha: More Noncanonical Scriptures, Volume 1 (TOC here). I have also published an article on it, "Scriptural Exegesis in the Treatise of the Vessels, a Legendary Account of the Hiding of the Temple Treasures," in With Letters of Light, the Festschrift for Rachel Elior.
More on the legends and theories about the Ark of the Covenant here and follow the links. More on The Treatise of the Vessels, the Copper Scroll, and legends and theories about the lost Temple treasures here and here and again follow those links.