Seems pretty imbalanced to me. The player with the bishops is forced to weaken his kingside/queenside pawns if he wishes to castle. Then again, having 4 bishops is overpowered as fuck, and I don't think four knights are any match for them. Anyway, who knows. I don't really enjoy this set up.
EDIT: Whoops, accidentally made it a puzzle. Oh well.
I wonder how viable interesting or workable chess would be as a game if instead of each player having 2 bishops and 2 knights that they had 4 of either, occupying the original squares as the pieces they replace. Such that:
PPPPPPPP
RBBQKBBR
or
PPPPPPPP
RNNQKNNR
Unfortunately, doing all my playing online at chess.com, not so easy to experiment with that. Not that it would be a very valuable exercise. Just idle curiosity more than anything.