The rule against strategic secessions is specifically because of the local recruitment advantage it grants. There is nothing else (that I can think of offhand) that making Iato the capital of a tiny realm allows Riombara + IVF to do that keeping it as part of Riombara allows Riombara to do.
That advantage will only be enjoyed by the nobles within IVF, which will never be more than a tiny fraction of those in Riombara, certainly not during the time frame the war is likely to represent.
No, but the rule does care about intent, when intent can be reasonably determined. Surely the fact that the creation of this realm has been declared as a goal for so long—and the fact that it would have been founded regardless of the war—is a strong indication of intent.
Not unless they can manage to come up with plans to secede the city years in advance, when the city is not even held by the realm they would eventually have to go to war with to take it.
To equate the situation in this case with one where Realm A says, "We wish to create a realm out of Keplerville! Therefore, we must declare war on Realm B to take Keplerville!", and immediately declares war on Realm B, is little short of absurd.
If the rule against strategic secessions simply forbid any secession while a realm is at war, that could be easily prevented in code. It is not, because that is not the purpose of the rule.
This is also true. However, when the strategic gains involved, in practice, will be quite minimal (if not negative), and there is a long public documented history of the realm in question stating the fully IC reasons for the secession, the label of "strategic secession" must start to come into doubt.
Again: If the rule were a simple, unqualified, "No secessions during wartime," there wouldn't be much doubt that this violated it, and your points would be valid. But that's not what the rule is, and your arguments seem to simply assume that a secession during a war of a city near the front will, ipso facto, grant strategic benefits significant enough to turn the tide in a war, rather than look at the actual facts of the case at hand.
"A year is okay" but "just before declaring war is not" is poor policy: how long beforehand does it need to be declared in order to be okay? Determining the legality of the move by how long ago it was declared only sets up arbitrary rules that no one can predict or understand.
And no, it would not be easy to code. Because not all secessions are made with the purpose of carving out the enemy realm. Duchies can secede by betrayal during war, or to avoid the fate of the central government, and that has nothing to do with plopping a colony in the heart of enemy land. This is what this secession does, however.
And I already named a ton of advantages seceding grants. At least now the city doesn't risk revolting just because it's so far from the capital and troops cannot make it on time for maintenance work. This alone is a serious blow to Enweil. IVF doesn't need to boast a huge army in order to push Enweil further down.
