Who doesn't know the charming "Inventory is full" or "You are over encumbered" messages popping up when you want to pick up your reward for killing some tough boss enemy. Now there is a solution for these kind of problems: the Backpack 3000!
To get a full overview of it's capabilities (along with testimonials and a list of famous people already using it) make sure to read the fact sheet.
Now seriously again:
In the last weeks we were working on our quest system and custom user interface (adding a journal for example). Tests with saving local data when travelling between levels were positive and we already implemented the basics of our persistence system that will enable free travelling between levels, while your progress and your modifications to each level aren't lost.
It's hard to give an exact date but expect some ingame video showing all of this around the middle of May.