Although Intel never explicitly expressed it, the general expectation was the impending 11th Generation Rocket Lake processors would slot fine into the current LGA1200 motherboard with the 400-series chipset. If there was any doubt, multiple motherboard manufacturers have officially confirmed the processors' backward compatibility.
ASRock, for one, has already updated various product pages to affirm support for Rocket Lake. The new description now reads "Supports 10th Gen Intel® Core Processors and 11th Gen Intel Core Processors (LGA1200)," with the latter alluding to Intel's Rocket Lake-S chips. Thus far, the preliminary list of motherboards (via momomo_us (opens in new tab)) includes the various offerings from different tiers, such as the Z490 Aqua, Z490 Phantom Gaming-ITX/TB3, Z480 Creator, and H470 Steel Legend.
On the other hand, Biostar reportedly shared a banner advertising Rocket Lake-S support on the brand's Z490 motherboards. The vendor has also updated the motherboard product pages to reflect the change. However, it would appear that Rocket Lake-S's rapport might only be with the company's Z490 motherboards since the B460 product pages don't proclaim support for 11th Generation chips.
While it's possible to enable Rocket Lake-S processors on all LGA1200 motherboards, we suspect that support will vary from one motherboard vendor to another. Besides the shift to the Cypress Cove microarchitecture, one of Rocket Lake-S's biggest attraction is PCIe 4.0 support. Nonetheless, some vendors might not have initially purposed some of their 400-series offering to support PCIe 4.0, especially the entry-level motherboards. That could be the explanation of why Biostar didn't mention Rocket Lake-S support on non-Z490 motherboards.
The current consensus is that Intel will probably take advantage of CES 2021 to announce Rocket Lake-S, which should come accompanied by new 500-series motherboards. Availability, however, is another story. If one Twitter user's roadmap (opens in new tab) is genuine, Intel might not commence Rocket Lake-S mass production until January 2021, meaning that the processors won't be hit the retailer shelves until February or even March.