Finally USB to 802.3bz adapters are available (2.5gbps at 50, 5gbps below 100 USD) I am wondering whether there are cheap solutions to switch 'em. Netgear has a few but even the GS110MX with only two multigig ports and eight gigabit is 200 USD. The cheapest multigig capable SFP+ transciever I could find is the MikroTik S+RJ10 at 51.