I'm not making a prediction. But I won't be surprised if the next Mac Pros all have HDMI i/o built in. In fact this may be a new and consistent feature of all the 2007 post Leopard Mac refreshes. The new upcoming not quite yet shipping Panasonic AG-HSC1U 1/4" 3-CCD 16:9 AVCHD PROLINE™ Camcorder with HDMI Interface and 40GB SD Store Drive is coming out of the Broadcast/Business division and it has no FireWire port.
That camera's HDMI output would be for uncompressed video. Anyhow, it's very likely that the camera uses USB to transfer the video data.
HDMI would be useful for a live feed. But feeding recorded material by HDMI to capture with your Mac would be a great waste of time and resources. Just transfer the data as data and transcode to the trusty Apple Intermediate Codec.
I found another link. http://www.camcorderinfo.com/content/Panasonic-Unveils-AG-HSC1U-First-AVCHD-Pro-Camcorder.htm