Sysctl under Linux is just a wrapper around /proc... and I'm not saying that the BSD guys got it wrong, but sysfs IS the strategic direction already taken by Linux. However, there are clearly problems with the status quo especially when it comes to atomic operations. Both of my proposals (multi-element sysfs nodes, and process private staging sysfs directory) are compatible with the evolving direction of Linux system resource management from userspace.
The scriptability issue around my private staging tree proposal is easily addressable by using some sort of token (futex/mutex/semaphone) based approach to opening the staging directory instead of a purely PID based approach. Perhaps I'll try a kernel patch to illustrate what I mean ... if I can drum up some interest.
One way or the other private staging of atomic operations (whether ioctl() or some variation on my proposals) is essential for certain operations, and trying to avoid it _will_ result in race conditions many of which have security implications as well... now that I think about it token based private directories would be cool from a temporary directory perspective as well especially if the OS automatically reaped the result after the last token holder exited... so many cool implications... :-)