Another bit of info I gleaned from PAX East. One of the buildings in the starting area had an "Ability learning machine". Interacting with it opened a menu with a long list of abilities, each one costing a single "Ability Point". The machine and the menu didn't look like placeholder, so it may be the intended system. I had one ability point so I bought a warrior ability that let me shoot a plasma ball once every 15 seconds. It was pretty long range and went through stuff, though the cooldown was annoying. Once I had it purchased, I could swap it with any other ability on my hotbar whenever I wasn't fighting. More interestingly, there was a button at the machine called "Refund Ability Points". It sounds like you'll be able to try different abilities pretty frequently, only limited by how many points you have and your access to a machine. Also, the unavailable hotbar slots had a tooltip that said "This slot will unlock at a later level". Most likely you get more as part of character progression. Case in point: The characters we used during the demo (which were level 6) had 5 abilities, while the Dev's demo characters had 6.