What about ability to specify a way of service/application activation by dbus?

[Nikita Zlobin]

There is one nice audio session manager, implemented as dbus service,
which starts another applications just by forking. This makes it more
like a desktop application, but its dbus nature brings one serious
trouble: when its daemon is started by dbus, it loses environment
variables, defined by desktop, which under kde are available for
anything, started by kde.

One bad result of that is sometimes wrong
application, proposed by xdg-mime (it may propos nautilus instead of
dolphin, konqueror or what ever specified by kde... i made simplified
xdg-open variant - fdopenres, which works better with such session
managers and is fixed a bit).

Dbus daemon could use customized ways to run various services (they
may vary from app to app). In cases like above application needs to be
started by desktop, and tools like kde-open, gvfs-open, exo-open and so
on may be invoked with command line, specified by services.