I'm not sure it's accurate to say thoroughly disinterested. I believe Father plans including it have got a respectable number of votes (though I admit my own bias might be colouring my memory), and the suggestion of doing it eventually has never exactly been unpopular, just other things have always been seen as more important and every time we start thinking we'll do it soon, events end up relegating it in priority. I think at this point, it will happen whenever we decide to use the Father again and not before unless events cause it to become very popular for unforseen reasons.Because Bretonnia is not currently in the project and a lot of people have been thoroughly disinterested in doing the thing that would have gotten them into the project. And we could get concessions form them, but it makes the whole 'good intentions' line very true, because then it goes from 'co-operation between nations' to 'we never brought you in, so pay up'.
I admit some bemusement whenever I see it taken as read that Bretonnia will join the Accords. While I am sure they can offer something or somethings to do so, they need to negotiate with 5 different powers (the Empire, Karaz Ankor, Ulthuan, Kislev and Lorelorn), all of whom need to agree if they are to join. Barring very impressive actions, that sounds to me like possibly being long negotiations. Joining the Waystone Project would be easier as they only need to persuade one person, Mathilde.