It is clear that you will have more granularity with the new strategy. But there are a few things you need to keep in mind
1) I hope you used 64K for ReFS? There are some threads here where 4K causes lots of pain for users
2) While ReFS will use block cloning API when you create a synthetic full (I would still do this) it will use less space, but I doubt that with your new strategy you will need less or equal space so make sure you have the storage available. In the end, you are still maintaining a full, lot's of incrementals, and then the (weekly?) synthetic fulls which should be indeed spaceless for most part.
3) make sure you have a method for testing your backups (Surebackup!) because if there is corruption on a block that is referenced many times, you could lose a lot
Hope it helps