I once lobbied a pair of blokes from IBM who had proposed an addition to the RFC for DHCP to specify the DNS suffix search list. Nothing ever came of it either.
That would be
RFC3397 specifying how DHCP option 119 is encoded, I assume?
As for it being proposed by MS, the cynic in me wonders if that was because they had a hole in their implementation whereby it might try to erroneously re-allocate an address. I'll let them off if so, it is good defensive programming and handles the case where someone's configured a static IP in the middle of the dynamic allocation pool. On the other side of the coin, there's an interesting denial-of-service attack there if you've got something sitting on the network that will respond to such pings from the DHCP server, such that it thinks the entire pool is allocated
