In an interview conducted over the official Valheim Discord, a developer was asked the question:

"With the massive support Iron Gate has received with Valheim, are there any other game titles you all will be working on after the full release, or will you instead dedicate your team to possible updates post-launch such as DLC?"

The developer answered:

"With the massive support we have gotten, it's important for us to stay focused and deliver a good game. After "real" launch we plan to keep updating Valheim with content. Also, all DLCs will always be free. We don't believe in paying for DLCs. Locking content from players behind moneywalls, WTF... It is pretty stupid and greedy."

The interviewer didn't specifically name which developer they spoke with, but I know that Grimmcore has also stated that all DLCs in the future, if there are any, will be free. Hope this helps! Skål!