I heard VRCSDK for 2022 will be VRCSDK 4.0.0 unofficially on github issues.
If the VRCSDK 4.x doesn't have any breaking changes other than supported unity version changes, I think changeing name of VRCSDK to 4.0 is not good.
There are multiple reasons.
First, many VRChat users know that VRCSDK2 to 3 has big breaking changes which force creators to re-create a lot of contents.
So, renaming VRCSDK will prevent creators to upgrade VRChat SDK version even if it doesn't need big migration.
Second, many tools has Avatars 3.0 as a part of tool name including curated Avatars 3.0 Manager. Renaming such tools will cause a lot of confusion for users, so it is difficult.
Finally, most description of assets / prefabs says "VRCSDK3 is required to use this asset." Please don't break this statement.