Currently we are using wcslib version 4.14 dating from 2012. Since then the library has been updated to handle more coordinate systems and the distortions from WCS "Paper IV". This includes TPV, which we would like to have because it is being used by the Decam community pipeline in their output images.
The update is pretty simple as the API has apparently not changed. afw compiles with the new version without modification, and with some fixes I have it returning coordinates on decam images.
This was previously discussed in
RFC-76, and it was agreed to separate the wcslib update from that RFC, possibly into a general update of afw::image::Wcs. I think we can go to 5.9 and get some of the benefit before doing the refactoring.
(Thanks to Frossie for the prompting the RFC.)