I don't think that troop presence works all too well. Players would just recruit small militia units to every region, or force courtiers, traders, etc. to have a unit.
I wasn't thinking of militia troops either. The peasantry wouldn't be impressed by militia, because the militia-men are their neighbors, not exotic visitors from other regions, clad in shining armor and bright plumage. The militia would also be a drain on the local economy.
And what's wrong with forcing Courtiers and Traders to recruit units? That's not covered by IR, and I don't see anything abusive about making nobles field troops. Just because a noble is a Courtier does not mean that he's not from the military caste. The nobility are "those who fight" after all.
Edit: Very few realms would have enough Courtiers/Traders to provide significant "troop coverage" by themselves.
