It will not be possible due to the limited capabilities of Apple's iOS. The same rules apply to Google's Android tablet OS.
A full Windows or Mac computer must be used if you own the music you are wanting to load to your watch. It must be done this way due to music copyright being digitally encrypted. The other option, is when you have a premium membership with Spotify, iHeartRadio, Deezer etc. with any of the streaming music providers that are partnered with our music onboard capable watches. In that case, you only need a solid Wi-Fi connection to be able to download your playlists from those services. Your watch will need to continue to have access to Wi-Fi since those streaming music services need to ensure you have an active subscription. Once again, due to music copyright.
