8940 has H470 chipset.  The next XPS 8950 will probably have H570 chipset while keeping the same chassis design as 8940, unless Dell is thinking of a totally new model.  Dell will likely continue to use the TFX psu up to 500w as they already did so in optiplex 7090 (Q570 chipset). If it is H570, the most significant improvement is PCIe4.0 or gen 4 for the M.2 ssd and x16 video card slot over H470.  Cpu support is about the same as H470 for 10/11th gen cpu, as Dell has updated H470 bios for rocket lake. The best Z590 chipset, AIO cooler, and 1000w psu for Dell will still be found only in AW Aurora R13 probably.  
When will there be a new XPS Desktop model? I think the XPS 8930 was released in 2018. XPS 8940 in 2020. Will there be a new model next year? Dell should release new model with since Windows 11 is coming. 
New XPS model?