Ok Helly, thanks for your reply, I appreciate it. Ill try to cover one issue at a time. First, extra buttons
The problem with a touchscreen is that you are forced into using the hardware buttons of the device for volume and sometimes this is not possible (or convenient) depending on how the touchscreen is used, mounted, what case you have, etc, etc (kitchen, bathroom, car, or outdoor use is a good example).
Although there are finger gestures for some functions, having buttons in Kodi is much nicer. It's one reason why CCM is awesome, because it has the Back and Home buttons at the bottom right which makes Kodi navigation with a touchscreen so much easier (although I must admit I always jump down there even when using a bigger screen and a remote too).
But for touchscreens, Mudislander kindly added (in CCM Gotham) Volume and Home buttons to several different locations.
These were optional in settings (to not upset other users), as were some 'large jumps' for each press of the volume button.
Some of this functionality is especially useful for radio / music, so that you still have volume control when audio is playing and you are at the home screen or navigating somewhere else in Kodi (to other music playlists for example), but I used the volume buttons on the full screen OSD all of the time too, since many videos seem to have a different volume level.
It also meant that Kodi volume can be independent from the device master volume - useful if you also have other apps running in the background too and don't want to affect their volume / notifications.
The video fullscreen OSD and pop up you mentioned doesn't have Volume or Home buttons in CCM Helix (they got missed in the change from CCM Gotham to CCM Helix unfortunately). In the screenshots you will see what I mean, and see the added Volume and Home buttons in various locations.
Hopefully you will agree it is worth implementing. especially with so many more people using touchscreen devices now.
Maybe some code from CCM Gotham might be helpful to make implementation easier?