I recently suggested another aspect of this which is a hotkey to do this for the SkookumIDE.
The button on the UE4 toolbar is also supposed to be triggered with a Alt+~ hotkey. (It somehow broke with new versions of UE4 so we are currently fixing it.)
We will make the SkookumIDE use the same hotkey to toggle to the UE4 editor.
We could add a button too as you suggest. Though many people stop using buttons once they learn hotkeys since they are faster to use. Buttons and menu options are good to learn the existence of hotkeys though.