I believe I've heard or seen that Nexus 2000 will be Gigabit only, as some presentations have shown funny ways of using e.g. Cat2960 connected to NExus2000 in order to support 100 Mbps ILO and alike.
I would imagine that in Data Centers the market for 100 Mbps is too small for Cisco to come out with a Nexus switch with that capacity, also because it would take out at least 1 10GE interface in the parent Nexus5000 - one could say that you'll be wasting capacity by doing that.
However, I do not have a clear statement from Cisco nor have I seen any links to info in that direction.
HTH.
