The release of the new CPUs will not be until later this year, but it is unknown if that availability in Q2 2021 (early March seems likely) refers to announcements or on-the-shelf availability as manufacturers are typically a bit squishy with that sort of language. So, with official support on certain boards being denied for the new chips direct from Intel, look for some possible “rebels” in the likes of motherboard makers (such as Biostar or Asrock perhaps?) to supply unofficial support for 11th gen. They’ve been know to do that sort of thing after all.
The latest chipsets will be H510, B560, H570 and Z590 of course, and what do they have over the previous generation necessary to support the 11th gen CPUs? Perhaps it’s the WiFi6 onboard? There are some differences in general support for high speed USB where some boards get faster (20Gb/s options on B560) while others appear to lose (10Gb/s ports removed from B510 chipset). One of the biggest draws for moving to 11th gen Rocket Lake-S for Intel fans, besides the performance boost, will likely be support for PCIe Gen 4, which all 500 series (and some 400) motherboards support in some manner.
In the end, there might be legitimate consideration regarding power delivery and VRM configurations on certain entry level 400 series boards, but not all. Early reports of power usage on 11th tell us that. But it does seem somewhat convenient to drive additional board purchases.
If you are piloting one of the entry level 400 series boards and expected to be able to upgrade to Rocket Lake-S based on previous commentary from Intel, well now you know better. I imagine that Intel thanks you for your contribution, but please buy another.