I like doing bolt on necks. As long as your neck pocket is nice and tight, you get awesome results. You can also easily raise the stack height increasing the break angle on your bridge. It also makes mounting electric pickups very easy since you have more room in the box.
I'm interested in acoustic CBGs only and experimenting a lot with the same Partagas boxes, to find out, which constructions sound better than others. I have two CBGs of identical boxes with identical sound holes, one neck through and one neck on top, both with the neck not touching the soundboard. There is a noticeable difference between the two: the neck on top variant is louder and richer in tone.
From other experiments I know that not only the sound board but also the vibrating bottom of the box is essential for sound. I suspect that anything that fills the space within the box will have some negative impact on sound.
So thumbs up for the bolt on solution if the box allows this construction and if it's realizable without another negative impact on sound.
Adjusting the neck angle is another topic, realizable with both construction variants; for adjustable neck through boxes see http://banjobridge.com/br-04a.htm how this is realized in an elder Framus banjo, scroll down to see a photo.
As far as made for sliding CBGs go I don't really see any advantage. For those of us picky players who like our strings as low as they will go then yes. Being about to adjust the angle of the neck is important. But the average CBG and player really would't benefit from a bolt on neck. The only bolt on neck i have is my Cosmic Glider. To be truthful I grab one of the neck through cigar boxes when I want to play. Haven't played the Cosmic Glider in months.
Now if your traveling a lot with them then yes. Bolt on necks would make packing them easier. Just put em back together when you get to where your going.
All my cbg's have been bolt on, or bolt in in the case of through necks, if you allow scope for adjustment, it really gives you a lot more options when you have playability issues