Overall, I think this is a very good suggestion. Very well thought out. Though I have a few things I would like to address:

  1. 1-I think that Nan Ungol, Black Uruk and Mordor Warg invasions should still be launched in Gondor and its fiefdoms, for difficulty reasons (although Ithilien and Harondor are in closer proximity to Nan Ungol, so it would make a little more sense for those guys to invade only those two biomes on rare occasions).
  2. 2- Considering that you mentioned Gondorian renegades, I wonder if the Mordor Warriors should be hireable, except through a quest.
  3. 3- I don't think it would hurt if the Morgul Knights would, very rarely, invade Ithilien.
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