Outside of cheap mass storage or just cheap storage, spinners have all but disappeared from the consumer space. Streaming and cloud storage negate much of the need for ever increasing drive space while the size advantage of NVMe is cutting at the desireability of spinners in most markets.Maybe when HAMR spinners have 4TB+ platters they may need greater than 600 MB/s. However 12Gb SAS already has this covered. I doubt this will have a large enough market in the consumer space for a SATA4 to be produced.
SATA Express wasn't the next generation of SATA. It was just a hybridization of PCIe and SATA.The next generation of SATA came and went. It was called SATA Express. It was a PCIe implementation of SATA which could transfer at speeds up to around 16Gbps. Unfortunately for the specification, NVMe devices started appearing about the same time and quickly became the storage interface of choice. The preference towards the latter was probably influenced by the fact that SATA Express only used two PCIe lanes while NVMe devices typically used four, allowing for far greater transfer speeds. Essentially, SATA Express was DOA. No more than a handful of devices in that interface ever saw the light of day. Technically, the U.2 specification (formerly SFF-8639) is an evolution of SATA Express, but this basically died immediately in the consumer market. The lack of adoption there was because Intel was really the only SSD maker that utilized it in consumer models. Companies like ASUS had U.2 connectors available on many motherboard models for a time, but when the SSD 750 series ultimately never got updated and no new models using the connector emerged, the port was dropped.
Technically, all modern SATA ports are actually SATA Express on the back end, but motherboard manufacturers opt for traditional SATA connectors instead of SATA Express or U.2 connectors.