http://www.gateworks.com/product/item/ventana-gw5310-network-processor
Out of price range in single units, but I don't know where the price breaks kick in. Dual-core 800MHz ARM should be plenty of power for the GigE ports.
I think to get any sort of platform like this by a major vendor, we're looking at needing 10K quantities, which I just don't see happening, without a really well-done kickstarter type campaign.
OTOH, a kickstarter might be a good way to get a largish group-buy together for some of these more dev-minded platforms.
-Aaron