Also getting lost here is the fact that Big Baby is going to be a much better player with the first unit, while KG will probably be equally effective with the second unit. KG can dominate a team's second unit and is probably better at getting his own shots. BBD in the starting lineup will be playing with the likes of Rondo, Pierce and Allen, so he can get his mid-range shots like he did in the playoffs last year. Also, playing in the starting lineup gives him the ability to play alongside Perk, who can make up for some of BBD's defensive liabilities. Meanwhile, the team is putting KG in with the second unit, which can compensate for Sheed's lack of defense.
This idea will never happen in practicality, but it is not absurd.