Hey, I’m maintainer for the rpm plugin, I’m not fully aware of the current state of the maven plugin nor am I familiar with that feature in Nexus.
Having said that, while you can’t have multiple remotes for the same repository (not only in maven, thats a genereal Pulp design aspect*), in theory you can have multiple “internal” repositories and aggregate their content in one main repository that gets distributed. Do you think that would work?
For example, in rpm you would use the repository modify API, which allows adding/removing content from other repositories / repository versions. While maven doesnt seem to have this endpoint yet, it’s probably an easy one to get implemented (IHO, easier than having multiple remotes).
In any case, you may open a feature request for your use case here and detail the requirements. It would be relevant to better understand use case for multiple remotes (if the alternative isnt enough).
* I remember hearing discussions about having multiple remotes for a repository in Pulp, but the discussion didnt get enough traction.