A feature request has been suggested as part of the testing of the YAML editor on staging.
Alias can be used to simplify YAML for a job group, and reduce duplication. But it can't currently be shared across multiple groups.
QAM could reuse aliases between YAMLs within Update|Incidents groups e.g. there are subgroups which could use YAML alias of tests running on all versions, another alias running only on sle15 and so on.
But that sounds like a layer above this. I.e. maintain your input in a git repository, expand the yaml to your linking and post it to the API for all groups. But expecting the UI to support aliases and includes is not what I think we should do.
Preprocessing sounds like a very interesting option as well.
Note this proposal is a long term thing. So if more people ask about it we have a ticket to refer to, and we can estimate the work for when we decide if we want something like that.
A wishlist item really, but I couldn't find a label for that in progress.