Big signs of continued story
When you finished your last mission your absolver was told he would be called again for assistance.
Also When you fight the last boss you can clearly see that there are two more doors on each side. Very nice placement for extending the map further.
I do agree with the quote at the end of the Guide telling us as new Absolvers that we would be called upon. I believe that it has something to do with a far off land with snow, possibly a mountain. The title screen has snow and up until the recent winter update we haven't seen any snow.
I do understand what you mean vaporwave,but the title screen shows the place you're in inside of the starting cinematic. Though I don't doubt there'll be a sequel, in fact I'd love a sequel.
edited June 2019
When you fight the twin bosses, they say they continue their beliefs. There could be an expansion for the Bird Callers Outpost or the Forgotten Temple. The story line could be explaining what happened in more detail.