Mark Darrah and Mike Laidlaw have both said that the Inquisition is "in opposition to the Chantry", with Laidlaw adding that the Inquisitor isn't a "puppet of the church". David Gaider said that the Inquisitor doesn't work for the Chantry. Cameron Lee was the one who specified that Cassandra broke the Inquisition away from the Chantry after the cataclysm that kills the leadership of the Chantry and the mages (who attended the peace meeting).
None of which have anything to do with your supposed Chantry disarray and power vacuum. I've never disagreed that the Inquisition is separate from the Chantry. Only that the Inquisition will, in any way, damage or supplant the Chantry, or that the Chantry itself is in any danger of losing its grip on Thedas.
Queen Anora is also willing to give the Hinterlands to the Dalish in respect to the sacrifice made by the elven Hero of Ferelden who came from the Sabrae Clan, and that wasn't "convenient" for her; she has progressive ideas. Also, I'm talking about a treaty between Ferelden and an autonomous kingdom of the Dales, not about the developers (possibly) handwaving the Dalish Boon; I have a fairly good idea that more than a few Fereldens wouldn't want to see Orlais wield the same level of power that it once had. We also know that the army will follow the ruler's command, as the Crown can provide support to the dwarves in the Deep Roads who are trying to reclaim lost thaigs.
Queen Anora or King Alistair, it doesn't matter. It was an extremely convenient act, and it ends the same way.
Monarch: "In reward for your service/sacrifice, I decree that you may settle in this land rendered almost completely uninhabitable by the Blight. Huzzah!"
People of Ferelden: "Nope. Not even in the Blightlands, knife-ear."
Monarch: "Oops."
If the Ferelden army is willing to tolerate going into the Deep Roads to fight darkspawn, I think they would be willing to tolerate fighting Orlesians.
You're going to want to reread the section you were replying to, because you misunderstood it. If the Ferelden people on the border with the Dales decided to instigate something with the elves, do you really think the Ferelden crown is going to send its army to put down Fereldens on behalf of those elves? No. Not going to happen. In addition to it being illegal in Ferelden to do so, Alistair/Anora would find themselves former nobility faster than you could say "Landsmeet".
The Dales and Ferelden are actually separated by the Frostback Mountains, and (it seems) the land mass that would connect the two through the Frostback Mountains leads to the entrance to Orzammar.
There are other passes through the Frostbacks, and, in spite of Amaranthine, there is still land trade that goes right through the Dales. Ferelden humans and Dales elves would be in constant contact with one another. Friction!
I think a treaty would help matters, and I'm not as pessimistic about it as you are, especially as Orlais is dealing with a civil war and the crisis of the Breach (that may substantially weaken it in the same way that the civil war and the Blight weakened Ferelden). That said, I don't disagree that the Inquisitor might need to take further steps to nullify the threat that Orlais can pose to Ferelden and the Dales.
Ferelden doesn't need to anger its populace, or other nations, by forming a treaty with elves. And if it did, for whatever reason, there's not a nation in Thedas that would blink an eye or think less of the Crown if they turned around and fed it to a mabari the moment it became inconvenient. They're just elves, after all. And even without a Dales buffer state, Orlais won't pose a threat to Ferelden again for years, possibly decades. The Civil War and the ongoing Nevarran threat make sure of that. Humans, however, pose a significant threat to the elves. And the people of Ferelden, with or without the blessing of the monarchy, will engage in violence against an independent Dales, and will aid other humans, regardless of nationality, in putting the elves 'in their place'.