FYI, with https://github.com/snapcore/snapd/pull/3998 installed (which changes KILL to EPERM), I disconnected the process-control interface and out popped the following EPERM denial:
Mar 06 08:35:45 sec-xenial-amd64 kernel: audit: type=1326 audit(1520346945.126:391): auid=4294967295 uid=1000 gid=1000 ses=4294967295 pid=11364 comm="pyrogenesis" exe="/snap/0ad/1/binaries/system/pyrogenesis" sig=0 arch=c000003e syscall=141 compat=0 ip=0x7fac57879d27 code=0x50000
and the application kept running. This makes sense because the default template allows setpriority for 0-19 and the kernel enforces via DAC/capabilities that non-root cannot use < 0, so the application tries to setpriority just in case it can, but doesn’t fail cause it normally can’t.
Put another way, this will fix setpriority for 0ad (and likely all non-root processes that try it) so that they won’t need process-control at all any more, let alone auto-connected.