Waiting this is implemented, you could do the following:

./Slicer --python-code "loadScene('/path/to/scene.mrml')"

You could also look at the available python API:
See https://github.com/Slicer/Slicer/blob/master/Base/Python/slicer/util.py#L136

Resetting to feature request, and noting that I really want this as well (mostly because my RSI is acting up and cmd line tab complete to load a scene is easier than mousing to File->Load Scene, select file, open).

For the scene files loading in from the command line, I'd like to request that they get loaded via Commit rather than Import (so direct load rather than adding them to the File Add Data dialog).
For data files, adding them to the Add Data dialog is fine, since the user will possibly wish to adjust names and other options.

Here is an initial commit that works in simple cases.

https://github.com/chrismullins/Slicer/commit/bfd9b3834872a24b47acf0810bf5630dd93f4e9c

Ideas: What if I want more than one file loaded? Perhaps something like ./Slicer /path/to/fileA.vtk /path/to/fileB.vtk should be implemented.
What if I want an entire directory to be loaded? Perhaps it should get a particular tag like ./Slicer --load-directory /path/to/DataDirectory

Now multiple files can be specified, and they will all be loaded if they exist.

https://github.com/chrismullins/Slicer/commit/8ad6ff4ba988263815f7fd38f10546e55985b16b

Fixed in r20699
See http://viewvc.slicer.org/viewvc.cgi/Slicer4?view=revision&revision=20699

Dear issue reporter,

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