It would be cool to have the possibility to group/ungroup elements

You can create groups using Scene->Create->Group, then you may drag shapes there using the scene tree panel.

Elements can already be grouped and moved in a group as far as I'm aware.

Yes although you can use the scene tree to group items, this is a much slower process than a program like Illustrator which allows you to click and group items very quickly. I often have to scroll a large scene tree panel to put everything in my groups together properly. Pointing and clicking to group and ungroup would be super quick!