dhcpcd-6.4.7 is hot off the press, the main improvement being mitigating the bash "ShellShock" exploit by escaping all characters as noted in IEEE Std 1003.1, 2004 Edition, 2. Shell Command Language, 2.2 Quoting except for the space character.
Needless to say, the entire BSD family is not affected by this bug as bash is not the default shell and to be fair a lot of Linux distributions are not affected either. If bash is your Linux distributions /bin/sh, OR you have applications directly calling bash, you should be telling them to get with the times as most people have since moved on to ash, dash or busybox for more efficient processing.
Regardless, shell is such an important in part of the system - it allows non programmers to "do things". Thanks to the dhcpcd hook system, a user was able to start tcpdump on hotplugged interface before dhcpcd actually started using it during the boot process. Why he wanted to do this, I don't know, probably for some debugging. But the point is, how would he have done this without shell hooks?
The important thing to take away from this is don't lock yourself into one technology - strive to be portable. dhcpcd works on many OS's, libcs, shells and userland tools. If any of them prove faulty, swap them out - including dhcpcd itself! But please at least tell me why you're swapping dhcpcd out so I can improve it :)
resolvconf was designed to take DNS inputs from many sources and allow the user to tailor these to their needs.