I've submitted my nfnetlink_log patches to DaveM earlier today. So what is this about? It's a replacement for ipt_LOG, ip6t_LOG, ebt_ulog, ipt_ULOG. It introduces a layer-3 (AF_xxx) independent way of logging packets via a userspace logging process.
Again, one step towards code unification. One new piece of code that replaces four existing ones (of similar size), and obsoletes the need for any other such mechanisms that might have appeared for other protocols later on.
If you want to see how to use it from your favourite userspace app, please refer to libnfnetlink_log.