They've already promised a "full expansion," and that's what they'll will be sticking with if they continue expanding it. Any "gameplay tweaks and changes" from expansions they want as a free patch.
"No, we want to do a traditional expansion, and we're in the early stages of planning for that right now. Part of the Kickstarter campaign was a full expansion, so we're definitely doing a Tales of the Sword Coast style campaign," they told us in our.
"We're still in the early stages of design for that right now, though. What I would say about additional content other than that, is that I would like to see any gameplay tweaks and changes we make in an expansion get rolled into a free patch. So if you don't want to buy an expansion, you get all the same gameplay benefits without the extra story."
Pillars of Eternity releases on PC March 26th. It is one ofhighest profile campaigns, which concluded with a huge $3,986,929 pledged by almost 74k backers in October 2012.