I have made mockups for a georectification tool for Wikidocumentaries at https://wikidocumentaries.wmflabs.org/wiki/Rectifying_maps. They are based on layouts for the Wikimaps tools that were never realized, and adjusted for the Wikidocumentaries architecture. It does not include masking yet, maybe we could reflect on what is created at the hackathon. I will be eager to work on the best practises for storing rectification information in Wikimedia projects.