It depends on what you are developing. rhino3dm is a library developers can use in their projects to read, write, and create Rhino geometry. If a developer needs to support Rhino 8 files, the it is a good idea to use the new stuff.
In this release we focused on updating the tooling to support the Rhino 8 file format and a few other infrastructural changes. We have some binding requests on our list. If there is something you are looking for, let us know!
Not for a while still. Weβre trying to figure out how to properly support running Rhino.Inside either a .NET 4.8 process or a dotnet 7 process. We just got this to work this week for Rhino.Compute with dotnet 7, but there is still a bit of cleanup to do.