It still only covers 50 or so skills. The other poster said that he had over 78 skills on his lone wolf. Then there are also the healing potions, the 5 resistance 15% potions, the resistance 50% potions, str potions, int potions, str debuff potions, int debuff potions, etc. not to mention the foods pizza, cheese bread, apple pie, dinner, fries, mashed potato, etc. and oh don't forget if you are an archer you have your 20+ different types of arrows... wait that UI won't cover everything either.
Agreed. That's why I believe the problem isn't the number of slots currently presented, but how difficult it is to sort out our skills/stuff and select them. And that's also why I believe Div1 UI is still a good source of inspiration in that department. There you had one button for selecting skills, one for drinking potions and one for changing weapons... and still somehow it felt right. Now we have 10 buttons to do the same things and that's not nearly enough.
Pitheco, it's a really nice mock up

The only limitation I see is when you start getting more skills per category, but it's a good fleshed out idea
Thanks for your feedback Songbird

About the limitation you said, this too has been noticed before and IMO I don't think it would be a problem that bad as there's nothing preventing the stacks of each category to occupy two columns or even being positioned horizontally. There certainly are many ways around having the skills go through the roof.