The details come from the Hammer and the Scalpel video, during the scene at the end with a giant message board detailing all sorts of potential Siege operators. A higher res version of the image surfaced on the official site, which gave the Siege community – including YouTuber coreross – a much better way to dig in.
One note, stuck over a map of Denmark, denotes an operator who is an “expert in covert reconnaissance and stealth tactics,” and has the “ability to blend and adapt into environment.” That’s stuck to the attacker’s side of the board, so we know what role this new Siege operator will fill. Ubisoft confirmed that Year 4 operators would lead off with the Danish op, and it seems the studio has provided a bit of extra detail here for a fresh hint.