I see the appeal of requiring matching funds for grants, and I don't really know how common it is for federal grants to require private sector matches (although I'm pretty sure it isn't required for, say, road construction), but I do find the inclusion of a 20% private sector match in the proposed rules for the Investing in Innovation fund to be disturbing. The Department of Ed is heavily staffed with people coming from and likely returning to big money "venture philanthropy" firms and foundations and for-profit corporations. This large matching requirement clearly adds to the power and influence of private philanthropy and adds yet another layer of interconnected influence between government and philanthropy.
There are a limited number of foundations and corporations who can provide matching funds of this scale, and unfortunately, they are closely aligned, philosophically and politically. Creating "i3" grant proposals without their approval and cooperation will be difficult, at best. There is a real risk that the range of acceptable innovation will be determined by self-interested actors in the private sector, not the public.