From Nicole:

Right now the Slicer execution model still passes fiducial points to
CLI's on the command line and doesn't take back output parameters. You
can pass points back in a parameter file, but they won't be
automatically turned into annotation fiducials (see the bug linked
below
for a link to the simple return types project page).
The plan is to extend the functionality once the fiducials are being
stored in a single file per list and CLI developers can read and write
the files via MRML storage node.

Related issue reported for Slicer3:

======================================================================
http://www.na-mic.org/Bug/view.php?id=648

Reported By: fedorov
Assigned To: millerjv

Project: Slicer3
Issue ID: 648
Category: Command Line Modules (Applications/CLI)
Reproducibility: always
Severity: feature
Priority: normal
Status: assigned

Date Submitted: 2009-09-25 14:43 EDT
Last Modified: 2013-02-14 15:26 EST

Summary: Passing ROI to CLI
Description:
I would like to be able to pass an ROI (vtkMRMLROINode) through the CLI
interface.

(0001254) pieper (administrator) - 2009-11-10 16:45
http://www.na-mic.org/Bug/view.php?id=648#c1254

Also need to be able to send fiducials back from CLIs...

(0001255) pieper (administrator) - 2009-11-10 16:47
http://www.na-mic.org/Bug/view.php?id=648#c1255

Perhaps there's a way to easily add a new storable data type.

(0001321) fedorov (developer) - 2010-01-30 12:20
http://www.na-mic.org/Bug/view.php?id=648#c1321

Jim introduced the capability to return scalars back from CLI. Follow the
development here:
http://www.na-mic.org/Wiki/index.php/2010_Winter_Project_Week_Command_Line_Module_Simple_Return_Types

From Winter 2014 Project week: 2 people have asked for being able to return fiducials from CLI modules.

Related commit:

See http://viewvc.slicer.org/viewvc.cgi/Slicer4?view=revision&revision=24812

<pre>
ENH: Improved ExecutionModelTour pointfile example

Fiducial node selector widget created for pointfile field does not support selection of multiple nodes
therefore adding a <pointfile multiple="true" ...> tag in the ExecutionModelTour example was misleading
(it will never get multiple files).
=> removed multiple="true"

Pointfile with channel="output" is a regular file field (same as transform, image, table, etc),
therefore adding a separate "File return types" section in the XML was misleading.
=> moved the field from separate section to right after the pointfile with channel="input", so now
it looks the same as all other file fields
</pre>

This feature was implemented some time ago. Markup fiducial points can be used as inputs and outputs (passed as files).