More than 2500 systemwide processes on OSX 10.9
Unfortunately it seems like maxproc is limited to 2500 with OS X unless you install OS X Server. With Server installed you can run the serverinfo tool to set high performance mode.

Just tried this myself and it seems to work.

$ sudo serverinfo --setperfmode YES
Server performance mode was enabled.


Rebooted.

$ sudo sysctl kern.maxproc
kern.maxproc: 5000


I didn't even need to change maxproc, after rebooting it was already set to 5000.