Personally, I posted this because Linux can now DHCP far faster, with both systemd-networkd and NetworkManager, and I thought people might find it interesting to read about some of the techniques used to speed up DHCP.
You wrote this in a previous thread as well, but never responded to my comment then. I have no idea why you are hyping up networkd's DHCP client so much, given that it was established that a) its functionality is a small subset of dhcpcd and dhclient, b) dhcpcd could reach comparable speeds provided additional steps unsupported by networkd like ARP checking are disabled and c) networkd DHCP violates and/or sidesteps RFC guidelines.
I've used dhcpcd, and I've seen many other reports from systems using it. It's an improvement over previous DHCP clients, but I'd love to see benchmarks demonstrating its ability to obtain an address in a vaguely timely manner. I have in fact seen piles of benchmarks for networkd, and I look forward to seeing similar benchmarks for the same code in NetworkManager.
In the previous article, I was particularly pleased that NetworkManager is finally starting to integrate good library code rather than spawning off programs and attempting to manage them. That's half the problem with dhcpcd: it really doesn't matter how fast it is, if it doesn't actually integrate well with a broader network management system. (And on most systems I've used, NetworkManager uses and depends on dhclient instead.) I hope to see more where that came from, and it's a toss-up whether networkd or NM will integrate good library-based wireless support first.
As for RFC guidelines, as far as I know the most notable one is one that every sane DHCP client violates, namely the massive timeouts, delays, and backoffs, all written for scenarios in which a thousand systems all come up at the same time and try to get an address over a network comprised largely of tin cans and string. Those guidelines matter very little on modern networks, compared to the cumulative wait time of millions of users on millions of systems.
Nope, I have nothing to do with CoreOS. I work on Chrome OS, and I wish Chrome OS used systemd; I don't enjoy fighting with upstart. In any case, I don't speak for anyone but myself, which really ought to go without saying.