I switched to KDE, so I won't be working on it anymore.
BTW: Plasma has such functions embedded (via "window rules") 😉
Maximize your windows vertical and/or horizontal (based on https://github.com/aXe1/gnome-shell-extension-maximized-by-default)
https://extensions.gnome.org/extension/2554/maxi/
git clone git@github.com:darkretailer/gnome-shell-extension_maxi.git ~/.local/share/gnome-shell/extensions/maxi@darkretailer.github.com