Comment 3 for bug 1596410

Fully supporting this request.
I did investigate how I could create such shortcut.
Here is what I tried:
1) from within inkscape, Edit > Preferences > Interface > Keyboard Shortcuts
But I couldn't find anything related to Text formatting, a fortiori nothing for sub/super-script
Related page:
https://wiki.inkscape.org/wiki/Customizing_Inkscape

2) read the top of this page:
https://inkscape.org/doc/keys.html
This led me to explore the default.xml, but there is nothing related to even the existing Text formating shortcuts such as CTL-B for bold text (listed in the keyboard shortcut page just above).
The default.xml says a custom shortcut can be defined from its "verbs", with "verbs" located in inkscape tree truck src/verbs.cpp. But in that cpp file there's nothing related to subscript and superscript, and nothing either related to the existing text KB shortcut (e.g. bold).

So even digging in the source of inkscape, it seems like creating this shortcut isn't an easy task. But I trust it is feasible.
If any one has any hint beyond what I've tried, I'd be happy to provide a solution.