... whether 'tis nobler in the mind to split yon bird down the back for your Holiday dinner or to suffer the beast to be roasted whole and unscathed?

What say ye?

I think it both brines and cooks better, but I still like the looks of a traditionally cooked bird!  Not a splayed turkey-hog!

I can barely get an 8lbr in my Jr. At that, the breast still hits to top of the barrel. So spatchcock is a no brainer for me.

I like em spatched but you can’t stuff them.

I've done both ways, but sticking with traditional whole bird this year,

Brining and going spatchcock this year. 

Going traditional and cooking whole. I'm sure it will come out great either way.

Has anyone done a spatchcock bone-in turkey breast?  If so how?

I will be smoking a whole turkey for the HOA dinner, but I want to do the turkey breast for ourselves?

I like em spatched but you can’t stuff them.

Stuffing a bird can cause issues with the inner part next to the cavity never reaching safe temps.  You have to be careful, to the point when the inner parts are at 165, but the breasts are at 175+. Never know when you get a bad bird.  But cooking it right makes a bad bird no longer bad for the major issues.  Can't fix bad relatives, hehe.

I always do the bird in a smoker with stuffing outside the bird.  I put sliced oranges/onion/garlic/fresh herbs/spices in the cavity walls in the cavity and don't cram it in, leaving a bit of airflow area.  I also only cook 10-12lb turkeys in a smoker.  I cook at lower temps for better juices and a juicier breast.

We make oven stuffing and the awesome cranberry stuffins muffins on Meatheads site.  Folks love them, creamy in the middle and browned on the outside.  Those DO go on the smoker with the turkey. 

Has anyone done a spatchcock bone-in turkey breast?  If so how?

I've done a couple small 7-9 pounders.  Just used kitchen shears and cut up eash side of the spine to remove it.  Super easy.
Then just forced it flat.

I flatten birds for the reasons already listed but I use a method that's different from spatchcocking.  See this thread.

Either way you flatten a bird, there's one additional benefit—it provides access to the internal cavity that allows more thorough cleaning.

I may, however revert back to spatchcocking because the removed backbone is useful for soup stock and I miss it.  We otherwise mostly waste it if we leave it with the carcass.

Here is a visual on how to do this.
Simple really once you see it.
https://www.thekitchn.com/how-to-spatchcock-a-turkey-cooking-lessons-from-the-kitchn-212641