It's beginning to sound like GNOME applications aren't even launched
by GNOME at all, but rather by systemd/dbus. Somehow.
GNOME Editor and other GIO applications work like how 16-bit Windows
applications used to work.
GNOME Terminal goes yet farther and not even the first instance is the
originally invoked process. All instances, even the first, are
"bus-activated". Depending from whether there is a per-user instance of
systemd or not, there may be a further level of indirection.
Of course, in the case where "bus activation" is configured to at least
pass things over to some proper per-user service management, the place
to set the ulimit for the likes of GNOME Terminal is in the per-user
service definition for GNOME Terminal server. With the nosh per-user
service mangement, this would be the
program. With systemd per-user service management this would be a
override for /usr/lib/systemd/user/gnome-terminal-server.service .
With nosh per-user service management, there is a
$HOME/.config/service-bundles/services/gedit service, which one can
start before attempting to run the first GNOME Editor instance; which
would permit one to place ulimit and suchlike modifications in
$HOME/.config/service-bundles/services/gedit/service/run . Vanilla
GNOME Editor does not attempt to plumb into systemd's per-user service
management, as GNOME Terminal does; so there is no systemd equivalent here.