Hi Kostas,
sorry for the delay and glad to see you’re willing to help out. :)
The problem is that the QTMLineWidget, which implements the line inputs uses Qt standard shortcuts. Basically Joris says that in order to solve this it’s best to ignore TeXmacs' keyboard shortcut system and hardcode a few standard shortcuts for the line inputs in each “look and feel”.
I think this is not such a great idea so he suggests we provide some method for the user to change the shortcuts for those line inputs only. Probably through standard preferences in preferences.scm.
I think it’d be best if the QTMLineWidget used the current shortcuts (that it can understand) to ensure consistency. This can be done calling (for instance in the widget's constructor) the scheme function kbd-find-rev-binding. To test it, in a scheme session type:
(kbd-find-rev-binding "(kbd-end-line)")
Notice that we use the string representation of the command, as given in the kbd-map. You can see all relevant shortcuts in progs/generic/generic-kbd.scm.
In Qt we need to reimplement the KeyEvent handler in QTMLineWidget and filter those key presses configured for left, right, end, start, etc.
If you finally find time to work on this don't hesitate to ask for help.
Best,