IIRC it has been said when we first went with the 343 under AW, that it suited our CBs better as part of a 3 rather than as a pairing because the extra man helped to balance their short comings as both a pair in a back4 and as individuals. Tactically it enables the centre CB to play more on the front foot and to step out to attack the ball in midfield.
As for a ball playing CB the same issue has seen a number of midfielders converted to play the role to bring the ball out from defence - Busquets, Mascherano, Martinez & there are no doubt others with varying degrees of success. I suspect AW was experimenting along these same lines when we saw the likes of Elneny used in the centre of a 3 man defence in pre-season.
IIRC one of the more successful such conversions has been Kevin Vogt at Hoffenheim, who not only brings the ball out from defence into midfield but also acts as their DLP in doing so as his passing is so good. Chapman did something similar with his 'WM', and also Taylor at Watford = both used accurate ball passers from defence, but it was interpreted as long/hoof ball rather than passing out from defence.