One thing that worries me a little with blockchain scaling is that the whole history is needed to guarantee its integrity. The blockchain will keep on growing, whether it grows fast or slow is not very relevant because regardless the same problem will arise which is data accumulating.
I've watch antonopoulos talk about scaling and compare blockchain to the internet, saying that blockchains will scale the same way internet scaled. This analogy is false imo, because data on the internet does not need to be permanently stored and that's the big challenge for blockchains.
Regarding your idea I think it's good but it is only slowing down the growth of the blockchain ( unless I missed something).
RE: The Concept of Hierarchical Self-Purging Blockchains Explained