If you're using a Thunderbolt based Mac you might consider using a Blackmagic Quad in a Sonnet or Magma PCIe to Thunderbolt chassis. I've heard of one person doing that successfully with the Sonnet chassis.
Blackmagic would have to modify their driver to allow one Thunderbolt input per port if you have a MBP Retina with two ports. Please ask them so they know there's demand for changing their driver.
TVS would also work with a Blackmagic Thunderbolt input device into Wirecast.