I think you're totally on the right track, Gil.
Me personally, I think that Howe wanted to take out the Couslands/take over their teyrnir, and he used the "They conspiring with Orlais, they must be taken down!" and played off of Loghain's paranoia. We know that Loghain had something in the works before Ostagar (probably keeping Anora on the throne, and not full-out regicide), because he poisoned (through Jowan) Eamon before Cailan died.
The Couslands are stout royalists, and if Eamon started publically calling for Anora to be set aside in order to produce a Theirin heir, they probably would have stood with him. So, if that's true, Loghain had reason to want to incapacitate the Couslands. Howe however wanted more... and so he played the Orlais card.
That's my theory and I'm stickin' to it