A great idea, but be careful on the amount of juice/honey you use. If you want subtle honey notes, obviously use less honey. If you want a mead with grape notes, use less juice. But don't mix equal amounts. You'll be making rocket fuel. You might want to split up two batches, one with more honey and one with more juice, and shoot for the same OG, that way you can see which is the better, and maybe even blend them later on in varying degrees.