LukasPrism,
I'm not going to comment any of that. I believe we have some UI designers here on the forum, and only if they would stumble into this topic, they would be able to explain us whether your approach is viable or not, from their professional point of view.
Personally, I hate when a sequence of actions is split between different UI elements and / or regions of the screen. I've seen software UI designed like that, and it only complicates things.
Well, at the moment you still need to consult your slots in the action bar, whilst choosing spells of appropriate level from the hotbar. There's still an assumption there that the user will understand the correlation. Admittedly it's not that difficult but where it does get messy is when you have repetition of spell icons when there are perfectly good buttons already on screen that can be used.
Filtering spells by the slots is a step in the right direction for sure. But it seems from what I've read so far that folk don't like the hotbar jumping around and changing, you're constantly reading around to find where something ends up. That's only going to get worse as we add more spells. Not to mention when you can also cast several spells from items.
