I figured out a solution to this problem myself that don't even involve modifying the Gnome source code. It is not what I initially looked for but it works perhaps just as well. In
/org/gnome/dekstop/wm/keybindings/ I just changed the following two settings:
switch-applications=['<Super>Tab', '<Alt>Tab', '<Alt>l']
switch-applications-backward=['<Shift><Super>Tab', '<Shift><Alt>Tab', '<Alt>h']
The first two keybindings are the Gnome defaults, whereas the last one is added by me. Of course, this has the (initially unintended) side-effect of bringing up the application switcher whenever I hit
<Alt>l, but since they're not previously used for anything, this could perhaps be a justifiable behavior.
The proposed solution works fairly well! I have tested it a bit and it suits my workflow (where I use
hjkl for just about everything, being a Vim user). However, I have "stress tested" it a bit and discovered two minor inconsistencies, which are due to the fact that the
switch-applications* events are not actually the same as the ones which are hard-coded to the arrows in the application switcher. First,
<Alt>Right will not bring up the application-switcher if it's not already there, unlike the recently proposed
<Alt>l. It seems to me a natural extension of the default behavior that they should. This can be fixed as follows:
switch-applications=['<Super>Tab', '<Alt>Tab', '<Alt>l', '<Alt>Right']
switch-applications-backward=['<Shift><Super>Tab', '<Shift><Alt>Tab', '<Alt>h','<Alt>Left']
<Super>Tab can be used as an alternative to
<Alt>Tab in Gnome (and likewise with the shift-key). Since
h) is not mapped to
lwill not work in this case. It would be an easy thing to add this, but beware that they are by default mapped to minimizing a window and locking the screen so you would have to remove those keybindings. Also,
<Super>Right is mapped to tiling windows to the left/right part of the screen. If you again want to use Vim-style
hjkl for these, you have three things
h) might be used for so you'd have to choose (unless you're up for some source code editing of the application switcher).
By the way, for those interested in using Vim keybindings in Gnome, I maintain a more complete set of keybindings in my Git repository at https://github.com/sigvaldm/gnome-dconf.