Having the option for multiple actionbars (like in the default UI). It would be great if I could switch between actionbars.

This already exists. Enable the default multi actionbars in the regular blizz options (interface -> ActionBars). Use the GW2 setting HUD -> Fade Action Bars to control whether they are always shown or only shown on mouseover.

For the main actionbar pages, use shift-mousewheel or shift-up/down arrow to toggle the primary action bar between multiple pages (yeh there's no UI element for this like the up/down arrows in default UI).