I was asked to make a camoflauged chocolate cake similar to the one pictured. The plan was for the cake to remain unrefridgerated until the party date.   My client (read friend) now wants to add coconut to the cake and I'm not sure what to do.  Do you think a coconut buttercream is a good idea?  I thought I could add sweet coconut flakes to it for the layers.

ideas or suggestions?

yes, chocolate and coconut are great together!  Add coconut extract (Taylor and College natural coconut extract paste is wonderful), coconut (finely shredded or chopped so easier to eat and cut) and a little coconut rum to your BC for a great filling.  If you are using ABC which is already very sweet, consider unsweetened coconut.  Lightly toasting the coconut really brings out the flavor.  HTH

I didn't think about coconut rum.  That's interesting.

I love adding liqueurs and flavored rums, etc to frostings.  they really add a depth of flavor and richness without tasting at all like alcohol.  Godiva chocolate and caramel liqueurs are amazing, banana and pineapple rum, and the more common kahlua, amaretto, limoncello, grandmarnier and chambord are all great and put BC over the top!  (I usually use SMBC).   

I don't know how you feel about using white chocolate ganache, but a couple of days ago, I made a coconut cake and covered it with white chocolate ganache which had little bits of coconut already in the chocolate and it is delicious.