What happens if you place the svg file in the root dir of your website and reference it there:
I seem to recall this working for me but it has been a year or so since I messed with it (was Sitefinity 5.4 or 6).
Yes i think that likely will work. It seems you just can't put specific mime-types in the App_Data directories where App_Themes lives.
We ended up just using a CDN so that worked for us. But we did move our webfonts outside of App_data and that worked for us. So i would assume that would work for the SVG's as well.
Sorry for arriving late to the party, but I found a workaround to this.
IIS7's URL Rewrite allows rewriting of outbound values as well as inbound...
<rule name="SVG" preCondition="SVG PC" patternSyntax="Wildcard" stopProcessing="true">
<match serverVariable="RESPONSE_Content-Type" pattern="*" />
<action type="Rewrite" value="image/svg+xml" />
<preCondition name="SVG PC">
<add input="REQUEST_URI" pattern=".svg$" />
^^ this basically checks that a file has a filetype of .svg on the way in (request), and then rewrites the Content-Type header to to image/svg+xml on the way out (response)
Just stumbled upon this thread. It's June 2017 and we're still facing the very same problem/limitation with Sitefinity 10 (10.0.6400.1 to be exact).
This workaround works like a champ.
Thanks very much for sharing!