Each time when switching a class, we have to reequip equipment, our passive abilities and the actionbar.

In a limited way this can be done by macros (too few commands per macro).

So why not store infos how a (for example) gladiator ist equiped with all of them, then when switching to another class, keep current state in mind and reload settings when switching back?!

With macros you have change them every time when you get new gear and abilities.
So you only have to equip them once and they are saved.