I'm on Windows and my co-worker re-compiled inkscape to include the console logging. I'm trying to execute the command but I'm getting an error message
I went to the location listed in the message but didn't see where to install the file or where other .theme files were stored. I found a GTK themes installer but don't see what that has to do with the operation I'm attempting. When I use the command
the operation is successful but the gui still opens and closes and takes a long time. I would like to fit the canvas to the drawing from the command line without opening the GUI. Any advice would be appreciated.

Got the same issue on a Ubuntu 14.04 LTS server running Inkscape 0.48 that is doing mass conversion from AI to SVG.
What is the best way to request the "FitCanvasToDrawing" feature be added as a command line only feature,
or is that problematic for some reason?

I've got no clue as to if that is problematic, but trying it yields

"WARNING: ignoring verb FitCanvasToDrawing - GUI required for this verb." and the program crashes (with an emergency save...)

The place to report bugs and ask for features is at https://bugs.launchpad.net/inkscape - please do a search first before you submit a new report.

Thanks for the information.
Here is the link to the question: https://answers.launchpad.net/inkscape/+question/295812