Perhaps... but it doesn't make sense to create incentive to secede just to recruit troops. You would still get better troops that way, but bigger nations shouldn't be so brutally punished for no reason, there are other ways to keep them in check with game balances, e.g. higher maintenance costs for government regions far away from capital/lower tax income.
I seriously think that it would change the game considerably for bigger realms.
It simply is a huge advantage if you can shorten your full recruitment refit times, which is military the main weakness of a big realm.
Although i agree we can limit such recruitment to just the recruitment centers in that duchy or city, it would still partially remove an important aspect of warfare against or with big realms.
The game allows big realms to exist, but it doesn't wnat big realms to fight wars on the other side of the continent.
Its above all very boring for everyone invovled.
The current mechanics try to force every realm to fight an enemy close by so the war is more intense, more risky for both sides and also makes gang bangs less likley.
Above all it will help new players gain h/p much quicker, be involved in a real war and thus hopefully stay in the game.
If my first experience of BM would be for example Caligan empire attacking some realm all the way up north id take me for ever to progress in temrs of H/p.
I'd be traveling more then fighting thinking they must have picked the wrong name for this game.
In fact i joined the game in late 2004 in the middle of an intense war between Caligus and Yssria, big battles would be every two days, i traveled not more then one or two region to bash into the enemy, and this intense conflict lasted for more then a year or even two if i remember correctly.
My character quickly gained the hp needed to check out other classes, become a lord or gain other positions as wel as recruiting a unit that actually mattered in combat.
I was also sucked into an exiting conflict that just kept me exited to play for every day, i'd even wake up early just for BM
I am sure this will happen much less if we allow more long distance wars by implementing a feature like this.