A post from CharlieIntel reports that the DLC will be "expanding on already existing areas and reusing assets," while Polish insider UV o grach made some similar comments on a livestream, referring to reusing assets and filling in blanks on a map.
"GOG and Michał Kiciński are aligned by a shared belief that games should live forever, " said Maciej Gołębiewski, Managing Director of GOG. "In a market that's getting more crowded, more locked-in, and forgets classic games at an increasing pace, we're doubling down on what only GOG does: reviving classics, keeping them playable on modern PCs, and helping great games find their audience over time"