yes, you should be able to tag a issue, comment, proposal or commit in proposal from a repository in a note (proposal, issue, comment) send to a different repository and have a reference to it and have it show up in both places.
Similar how it works 'mentioned in' in github I suppose. 
this is dependent on this issue and:
nostr:nevent1qqsg9fdqq7djq2sc7xamt49n7zd5qu73y8pupxfqxm3s76j3r25shqqhtk8jp
https://gitworkshop.dev/repo/gitworkshop/issue/82a5a0079b202a18f1bbb5d4b3f09b4073d121c3c0992036e30f6a511aa90b80
and