The i7-7700K has only 4 cores. The comparison with the 6900K is more fair.
Why is single thread more important in development? Large project builds typically spawn as many compiler processes as there are CPU cores.
Otherwise, your cores will be either waiting for something or just getting hot running synthetic benchmarks.
All the other chips have 16 PCI-E lanes, which you max out just with the graphic card.
Where I live, the price of a 256GB NVMe drive == 512GB SATA drive :(
It's also pointless if consumers will be choosing between a 7700K and the closest equivalent Ryzen part.