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 versionTomas commented
Just commenting, I've switched to Pocket Casts due to this. But I'm not totally happy, if you implement it, I'm coming back and donating.