Well this is interesting.. in my delegates file, there's this:
<!-- Remove the extra space in - -export in the line below when you want to use inkscape -->
<!--<delegate decode="svg:decode" stealth="True" command=""inkscape" "%s" - -export-eps="%s" - -export-dpi="%s" - -export-background="%s" - -export-background-opacity="%s" > "%s" 2>&1"/>-->
Which isn't exactly the line you've posted, since this one is exporting EPS, not PNG. But after removing the extra space and un-commenting the line, it has no effect. I also tried pasting your line into my delegates file, and nothing is changing. Magick is still using RSVG and not Inkscape.