Go for it. Dart does amazing work that I have admired from afar for many years...Problem is, I've never heard one of his instruments (sigh).

Koa back and sides would probably look great, and I am of the opinion that back and sides contribute very little to the overall tone of a mandolin.

Try to play a few instruments with different tops, like European spruce, Italian spruce, Englemann and Sitka spruce, Redwood, Cedar...the whole gamut of the musicwoods. Somewhere there is a wood that will sing to you, and you will know when it happens.