Is it possible to add it in the future ?
Not unless Apple change their Terms of Service.
From previous information shared on here when this was requested for Spotify, the reason I understand this is not possible isn’t because of technical limitations, but because Apple’s ToS forbids apps from accessing the data of another app, i.e. djay cannot access data stored by Tidal/SoundCloud/Spotify, but streaming this data within djay is not restricted by the ToS.
It is possible to realize the offline mode for Tidal. If you have a Tidal music downloader like TunesKit Audio Capture, you are able to download Tidal music and convert Tidal music to several universal audio formats like MP3. Then you can use Tidal music in DJ software anytime even without an internet connection.