Cascade Lake-X will keep the core count at 18 cores but will expand the number of PCI Express 3.0 lanes from 44 to 48. The chip is still made on a 14nm process so in terms of pure performance gains we aren't expecting major gains.
However, Intel does promise that users will see very big gains in relative performance per dollar. In the slide below, which got shared by Dutch tech site Hardware.Info, the chip giant claims Cascade Lake-X will offer 1.74x to 2.09x higher performance per dollar than Skylake-X. This implies the pricing of Cascade Lake-X will be significantly lower than Intel's current HEDT lineup.
Cascade Lake-X continues to use LGA2066 and should be compatible with existing X299 motherboards (after a BIOS update).