Currently, we write one file per gear in /etc/security/limits.d, when in practice most gears will be left at the default settings. It's possible to specify a pam_limits rule by uid range. According to the limits.conf manpage, the "domain" field may contain "an uid range specified as <min_uid>:<max_uid>." For example, if GEAR_MIN_UID=1000 and GEAR_MAX_UID=6999 in node.conf, the nproc entry might look like: 1000:6999 soft nproc 250 The performance benefit of opening one file instead of several hundred may not be large, but this also makes it easier for an administrator to see which gears intentionally have non-default values set.
The Throttler rewrites these individual files depending on gear usage. Maintaining and rewriting one file would be prohibitive.
The nproc limit is not rewritten by the throttler last I checked. Perhaps that has changed, but even so, the throttler can write files for "throttled" gears and remove them to unthrottle, and this would be manageable and a huge improvement.
After discussion with Andy Grimm, this is being closed as WONTFIX due to low priority.