There are several pressing problems including the redesign of the events system, having fast non-persisted values during block import, managing complexity in the transactional storage system and dealing with large code blobs in PoVs, as well as paving the way to useful GPU utilisation. These problems are all related to our over-reliance on a single large fixed persistent cryptographic data structure - the State Trie.
New storage primitives are needed in order to solve each of these issues effectively and efficiently. A new issue has been opened in Github putting forward a proposal for a minimal new host interface which should allow for this to happen. This may be of interest to the Polkadot builder community.