Comment 12 for bug 478737

some notes while searching for related info:

a) Inkscape 0.46 and 0.47(pre) show the same behavior:
  - baseline-shift is not supported by the renderer
  - it cannot be added as CSS style property in the XML editor

b) as long as you don't edit the text element in Inkscape,
   the CSS style property is not stripped when saving as Inkscape SVG.

c) adding as CSS style property to <tspan>
   <tspan style="font-size:12px;baseline-shift:super">st</tspan>
   with the built-in XML Editor fails with this Inkscape console message:
WARNING **: Unimplemented style property SP_PROP_BASELINE_SHIFT: value: super

d) adding as separate XML style attribute to <tspan>
   <tspan style="font-size:12px" baseline-shift="super">st</tspan>
   with the built-in XML Editor works but the attribute is still not
   supported by the renderer.

other links:
Inkscape Wiki: CSS Support - Updating for changes to <style> content
<http://wiki.inkscape.org/wiki/index.php/CSS_Support#Updating_for_changes_to_.3Cstyle.3E_content>