It appears that after many months of Google keeping tight lipped over the future of Google Play Music they have added migration functionality to YouTube Music to allow Google Play Music customers to migrate their uploaded music collection, settings, personalisation etc. from Google Play Music over to YouTube Music. Coinciding with that announcement has been a tentative timeline on when Google will be phasing out Google Play Music (link) which at this time is scheduled to be shut down by the end of this year (link).
I’ve given it a go – the uploading process is drag and drop, and yes you can select multiple folders and they will upload the contents of each of the folders. In my case what I decided to do was upload the original FLAC version as to avoid lossy to lossy conversion so that it is only a lossless to lossy conversion which should avoid the sorts of audio qualify degradation associated with transcoding between lossy formats. So far the audio quality is as good as the encoding I have done on my computer (I use dBpoweramp which makes use of the built in AAC encoder which comes part of macOS).
I’m also having a look at Google Drive and how it compares to Microsoft OneDrive – I’ve got my stuff backed up my on external flash based storage but I always like to have a second backup just in case the old proverbial hits the fan. The benefit of those two options over iCloud is firstly it downloads everything whether you like it or not – of course Apple say that it does it ‘intelligently’ but for me I don’t want it downloaded until I need it otherwise it just sits there consuming space. In the case of OneDrive and Google Drive they only download when you try to access it thus minimising the amount of hard disk space that it uses it not to mention not having to worry about whether your computer is silently downloading in the background while on a metered internet connection (see tethering to a mobile phone as a good example of that).