Does the NIC in your 5150 connect to a 10 gig switch?
In fact it does...obviously not on the 10gig ports (there are only two anyway, and they're in use), but yes, it's talking through a 10baseT AUI transceiver to one of the 1gig ports in a Cisco 3560E. Works fine, unlike some of the cheaper 1gig switches that don't seem to like it (not sure if it's the 10baseT or the half duplex they don't like). So, in that sense, some manufacturers have already "dropped" 10baseT support!
But anyway, what's a 5150's Ethernet capability have to do with why do we need an intermediate speed with a slightly incompatible standard, when 10gig is established and available?