If you look up on the official website, 4 lords are shown that would likely be in skirmish, one being Ysella.
I can only speculate, we get more lords during Early Access as it moves forward to the 1.0 version, adding the Wolf, Fox and Toad. I think the Wolf doesn't need to appear in the campaign and if so, perhaps just for a short appearance in the final cutscene until the credits rolls.
Yes, I saw that in your thread, including mercenary units Firefly hasn't talked about yet. But Stronghold games always had stuff ghosting in the gamefiles, that were probably planned until Firefly scrapped them. An example is the Caliph and the four dukes having audios files of their messages inside SH2's files and SH3 even had more stuff that has never been used since the game itself is still incomplete, I think you even did a thread of it long ago, searching the datas andalot of stuff was found, including a planned skirmish mode?