RDP has not been discontinued, but is now hosted elsewhere. It is at least available in source-forge. In fact, you can use the RESCRIPt plugin to fetch the latest version of RDP following this tutorial.
You can also follow our SSU tutorial for GenBank.
Assuming the rank designations are similar, and they do not differ too much with their taxonomic schema, you should be able to merge the taxonomy and sequence files together, then make a classifier. I've not tried this before, so I cant comment on how well it'd work.
The closest thing I can currently think of, you can try is the feature-classifier classify-consensus-vsearch with the --p-top-hits-only flag. I am sure someone else might be able to provide a better or more creative solution.
You can also consider using the weighted classifiers constructed through q2-clawback.