The selfish part of me says, "skip to the end." In other words, the BAT, that is because I will never live to see it, nor will a lot of his other loyal fans at this current rate. And as you point out, he will be in his eighties if he continues on his current timeline for getting the books written.
I also think the series would benefit from editing, some of the story lines have suffered some from sprawl. It is also true that Jim wants to write other things, I understand that, but I think it has come at the expense somewhat of The Dresden Files. The long stretch between Skin Game and Peace Talks is a perfect case in point, making loyal fans wait years for the next book in the series isn't fair. Only Jim can answer why the reason for that was, but that cries out for edit,edit,edit!
I think Jim has caught himself in his own trap of, "wouldn't be cool if...." So yeah, having Harry involved in a novel with a pro-wrestling story line seems cool, but how far is it taking us down the road to the BAT? Both Peace Talks and Battle Ground only seemed to present more questions than answers exploding in ten different directions at once, leaving a lot of story lines just dangling perhaps never to be resolved.
I don't want a rushed version of the series, and nor do I think Jim should be chained to his desk. For it to even exist, let alone be it's best version, he has to keep loving it. And nor do I think I am in any position to advise or ask Jim to do anything with the series. This is just my thoughts on the subject and want to see what those of you around here think.
I agree, and I'm not alone in this, many of us have felt that the latter books have a "rushed" quality to them or going through the motions quality.. No, Jim shouldn't be chained to his desk, but is that the real problem? I mean he managed to begin begin one series and finish another since he has been writing The Files.
Finish Twelve Months (assuming he has already started, or if he feels he needs to write it etc). Then straight to the BAT, and all the other case files come out after the BAT or as short stories in between and/or after or even just get shrunk down and included in the BAT. To me, the Dragon fight and the Kaiju stuff would be fine in the BAT. The pro-wrestling feels like it would be just as good as a side story, unless there are major cosmology and/or plot reveals in it. Mirror Mirror does feel like it NEEDS to happen, just because the multiverse stuff is going to be so important. Which is why it would have been good as the next book, but I understand that there are important character reasons for Twelve Months (and Jim clearly feels strongly that this book is important to him to be written, so it's hard to not have it now).
Yes, Twelve Months is an organic outflow of dealing of Harry dealing with his grief and the fall out of how Murphy died. That makes sense, the problem is all the other story lines introduced at the end of Battle Ground, Marcone/Namshiel, Thomas/Justine/baby/Nemesis, break with the White Council, break with Ramirez, dealing with Eb, Stars and Stones and WTF is the purpose of a star born, oh and marriage to Lara.. That is what I mean by sprawl, any one of the above almost deserves it's own novel, or at least a short story, something is bound to get lost. We are still talking about Elaine and Cowl, are they just to be left as dangling story lines never to be resolved? At the time they were introduced they seemed to be pretty important.
Yup, skip to the BAT.