One of the first times I played with campaign modding I did something
very similar to this, biggest difference being that I had the Harad/Corsairs succeed in dominating western Gondor & I upped the aggression between Dunland, Harad & Adunabar. I also included more Palantir & Blades of Westerness, purely for my own enjoyment... I did also include a mixed stack of Dwarves, Elves & Dale troops (a rescue party for the RK, if you will) but I had played around with these units within the standard campaign previously anyway.
One problem I did have (and this is because I'm a sticker for trying to keep the three great Houses about - in my current game the House of Hurin is now no more

and the role of Steward & Prince of Ithilien has passed to a sub-branch of the House of Galador) was that there wasn't a huge number of births within the family members. I think this is because the number of generals within your faction is directed linked to the number of provinces your faction controls - the more provinces, the more family members born. As a rule I never accept adoptions, Man of the Hour events or female family member marriages purely to increase likelihood of male births within the Great Houses and thus maintain the lineages.
Was a great scenario though and didn't take much to do. Copy the_new_shadow folder, alter the decr_strat.txt file and you're there. Have fun reclaiming Pelagir & Minas Tirith!
Edit: After reading another thread here, maybe an Adunabar presence in western Gondor might be interesting, rather than Harad/Corsairs... A counter revolution in eastern Mordor, back to RK from Adunabar, Rohan dominance in Rhovanion & Dunland, Adunabar dominating Rhun as a protectorate - the possibilities are endless really.
This thing all things devours:
Birds, beasts, trees, flowers;
Gnaws iron, bites steel;
Grinds hard stones to meal;
Slays king, ruins town,
And beats high mountain down.
There is never enough of it!