Alder Lake-S is rumored to feature an up to sixteen core design, based on ARM's big.LITTLE principle. This means you get eight high-performance cores as well as eight smaller cores with high energy efficiency.
While LGA1200 is compatible with LGA115x coolers, which uses a 375mm x 375mm socket, LGA1700 uses a larger socket that measures 450mm x 375mm. This implies existing coolers may not be compatible with LGA1700. Citing Asian rumors, WCCF Tech writes LGA1700 will likely have a longer shelf life. It's believed that future chips on LGA1700 will introduce PCI Express 5.0 support - but DDR5 support should not be expected:
The LGA 1700 platform may get PCIe 5.0 support in a later revision but DDR5 support should not be expected. The LGA 1700 platform is also going to feature a higher number of PCIe lanes. Based on this information, we can see that the 500 extra pins would enable higher PCIe lane communication and a wider electrical configuration that will accommodate the hybrid chip architecture featured on Alder Lake CPUs. The larger chip size can also hint to a chiplet based design rather than a monolithic die.