In case anyone is interested The Verge released the following article a few hours ago, which is interesting and can be found here. Small excerpt:
The Verge has recently learned that Spotify HiFi has been ready to go for more than a year. The technical work to bring the feature to market is largely complete, and the company has re-ingested its entire music catalog in lossless quality. Spotify employees have access to HiFi. But since it was originally intended to cost more than the standard plan (and thus boost Spotify’s average revenue per user), the launch was spoiled by Apple bundling lossless into Apple Music for free. If you read into Söderström’s answers, it’s clear that Spotify doesn’t intend to do the same. You can now expect HiFi to eventually appear as part of a more expensive plan — likely one that also includes spatial audio/Dolby Atmos and other perks related to audiobooks and podcasts.
The when remains naturally unclear. "Educated" guess is 2028. And if I remember correctly, Spotify HiFi will be CD quality bit rate.