I’ve seen it done on Oracle before like replicating 11 -> 10 or 11->9. The intermediate format for GoldenGate has been standard forever, so as long as you have GG binaries certified to connect to each database then theoretically it should be possible to get them to interact with these intermediate files and extract or replicate as needed.
I'm a fan of SQL Developer, have been for years. I especially like User Defined Reports. Time for some shameless self promotion!
Certificates can be a pain.