The municipality of Gothenburg has given the go-ahead for the hotel and water park. Construction is expected to begin in 2019, and will be completed in 2021, the same year Gothenburg will celebrate it's 400th birthday. The cost is about 2 billion SEK ($230 million, €210 million). The hotel and water park will (probably) be themed around the Swedish East India company: https://en.wikipedia.org/wiki/Swedish_East_India_Company
The investment is expected to increase the annual number of visitors to Liseberg with 600 000.
Edit: Apparently it was the municipal board that had given a go ahead, the project still needs approval in the municipality council. Though that shouldn't be an issue since a vast majority approve the project.