Hmm, let's structure this like this, instead?

array(
  array(
    'daemon' => 'PhabricatorRepositoryPullLocalDaemon',
    'arguments' => array('x', 'y'),
    'copies' => 8,
  ),
  ...
)

Right now, there's no room to add keys we might want to add in the future, like nice (T4804), user (switch permissions to a user), debug (verbose mode for just one daemon?), env (set environment?), cwd, you can't start several copies of a daemon with arguments, etc. We'll probably only ever implement 1 or 2 of these, but they seem like reasonable things this might want to provide some day.

Beyond that, one major downside to this approach is that installs which adjust the configuration slightly (to launch more or fewer taskmasters) will no longer receive updates to the default configuration: if we add "FactCursorDaemon" in the upstream next week, any installs which have adjusted the taskmaster count will completely override the new default configuration with their adjustments.

Offhand, I don't have a great solution to this, but it seems like a significant problem. One possibility is that we could implement merge rules for the configuration, and read all the configuration levels, overwriting key-by-key at each level. This would survive the addition of new daemons, but not adjustments to default arguments.