I think M.2 is fine, plenty of empty space between x1/x4 slots begging for something to put there. Access may be annoying but most normal people won't change the SSD more than once or twice over the board's useful life so that isn't so much of an inconvenience.
That said, it would be nice to have "SATA4-Express" to bump 2.5/3.5" storage to 12-16Gbps, maybe even upgrade the connector to x2 signaling for 24-32Gbps.
I concur, we need at least SAS 12 Gbps to be ported over to SATA4.0 with built in NVMe capability and push HDD makers to go Multi-Actuator. Maybe throw in some 16/32 GB Optane to help as a buffer.
Stop being lazy WD, you heard me, if Seagate can go "Multi-Actuator" and deliver higher linear throughput, you should be able to as well.
And bring back 15k RPM 2.5" HDD's with "Multi-Actuator", get some real Linear R/W through-put.
Stop holding back HDD technologies. Stop being quitters.
You don't want low end QLC/PLC SSD's to eat your market, start delivering at least some linear through-put.
We don't expect much Random IOP improvement, but you can stand to improve Linear R/W through-put and max out that interface =D