Wing dihedral in a biplane
There's a line of airplanes that have already done it, at least a bit.
The Rutan tandem wing Quickie designs are exactly that configuration, except that the wings are radically staggered because the forward one is the trimming/pitch control surface, and the dihedral/anhedral angles are shallower.  But looked at from straight ahead, there it is.

The anhedral of the front wing is mostly there because that's where the wheels go. Versions of the 2 seat Q2 that have a conventional tricycle gear, have a nearly straight lower wing because the most of the anhedral is &quot;in the way&quot; (tips near the ground become a problem now without wheels there).
The problem with the configuration is other than being able to put the gear at the wing tips in Rutan's application, there's no point to it.  That anhedral wings cancel out the dihedral wings, form a roll stability perspective, making the result more or less the same as making all the wings straight.  If you do want to put the wheels there, you have to make the spars do double duty as really long leaf springs (bending loads from landing are much harder on the spars than flight loads), and there are ground handling issues with the wheels so far apart.
So might as well avoid the hassles of fabricating bent spar beams and make them straight across in the first place, or at least with more normal dihedral angles. It's more or less just something that looked cool from a science fiction perspective.