The next couple of versions will focus in getting reed of any existing issue, then I will resume working on this feature.
I may have found a solution to handle the charge necessary and which might not cost too much.
Once a first beta with basic subscription syncing is available I will study the impact on the servers (and the cost), then I will add more syncing step by step, in order to sync the read status, favorite flag, playback progress, …
Hopefully I’ll be able to add this feature in the free versionAnna commented
I think you can now synchronize with Google drive without having to pay anymore. It's like a hidden storage like what's app is using or so.