Rosetta for ARM64 to x86_64

It's possible, yes. But not necessarily practical. The demand for it just wouldn't be there.

With the large installed base of Intel Macs out there, developers will most probably compile and package their applications for both, at least for a while, and gradually migrate to Apple Silicone only as the installed base changes.

Are you asking if they can create a reverse of Rosetta 2? Why would they. If a developer compiles their applications correctly it will run on both x86 and ARM processors.