http://www.independent.co.uk/news/world/middle-east/lost-languages-found-ancient-manuscript-parchment-saint-catherine-monastery-sinai-peninsula-egypt-a7916346.html
all clever stuff
With the right equipment and sufficient scholars, it might be possible to check every palimpsest in every collection.
I wonder what the Vatican Library might reveal.
the mind boggles at what is possibly waiting to be 'discovered'
The thing needing scare quotes would seem to be "lost" - Caucasian Albanian, while obscure, is by no means unknown, and may even have a modern descendant in the Udi language (https://en.wikipedia.org/wiki/Udi_language).
(The only other language explicitly said to be found in the palimpsets is Arabic, which is about as un-lost as a language can be.)
Now we just need them to find a legible version of Claudius' Etruscan History or Ctesis Persica, or similar lying under another copy of some religious text.
the list is endless of wished for and now lost manuscripts...! :)