I got tired of not knowing what speed I was currently playing at. So I edited the Plex for Kodi plugin. There is a pull request here (but I doubt it would ever get merged):
If you want to start using the changes yourself grab this xml file:
Upload it to this folder (overwriting the one there) /sdcard/Android/data/org.xbmc.kodi/files/.kodi/addons/script.plex/resources/skins/Main/1080i/
Then grab all the OSD*.png files in this folder:
Upload those to:
/sdcard/Android/data/org.xbmc.kodi/files/.kodi/addons/script.plex/resources/skins/Main/media/script.plex/
Now when you change the playback speed you will get a cool round icon on the top left that tells you your current speed!
Joseph Elwell.