This post discusses the 2nd flag-day putback yesterday, which is Brussels (phase I). Brussels also changes the way NIC drivers are administered, but it is focused on simplifying and centralizing the administration of network driver tunables -- these are the values used to tune the device itself, or in some cases, the link layer properties. The most common of these tunables are the values associated with duplex and link speed settings.
Historically these values have been configured with ndd(1M) or driver.conf(4). Many people know how I feel about those methods, but let me just reiterate: "ndd must die!" (And driver.conf, as well.)
The Brussels putback represents another opportunity for community members interested in kernel programming though. A lot of these NIC drivers need to be converted to use the property access methods that Brussels offers, and have the ndd support ioctls removed. (And yes, I strongly desire to see the ndd(1M) ioctl support removed from drivers. A follow-on phase for Brussels will offer ndd compatibility at the Brussels layer.)
Brussels provided a conversion of bge(7d), but many other NIC drivers remain. I plan on converting my two drivers, afe(7d) and mxfe(7d), as well as a few drivers that are still closed source (iprb(7d) and rtls(7d)). But there remain many others. And conversion of a driver to support Brussels is just the sort of bite-sized task that is great for learning how to develop in the kernel. Some possible drivers to convert are sfe(7d), rge(7d), and nge(7d). If you're interested in working on one of those, let me know (you need the hardware, though!)