Last two core sets had 22 and 23 artifacts, plus 6-8 nonbasics. I don't see room for multicolor.
Well, we know we have at least one multicolor card in M13, although I suppose that isn't a great reason to assume that there will be more. Also, the last two Core Sets were on either side of an artifact block, so maybe the number of artifacts was inflated for that reason? I don't know what the numbers from previous Core Sets were like.