I really don't see 'Inverted full backs' being much of an issue, particularly defensively. We are talking about professional footballers here, players who are perfectly capable of using both feet. They don't need to be particularly accurate with their weak foot in that position, most of the time it'll be a simple pass down the line or a booted clearance.
However, the 'downside' to this is when you consider how Bong contributes offensively, as he regularly overlaps. Playing a right footed player on the left side will likely reduce penetration down that side, and if they do overlap, the quality of the ball coming in won't be quite as good.
That would be a good idea. When I played football, if I tried to block a cross with my left foot, I'd probably fall over.
Tangent:
March 12 shots this season all with his left foot.
Lualua (in half a game less time) 22 shots, 11 with his left, 11 with his right.