If you type #, then you search throughout your whole workspace to try to mention right thing. But if we could set a custom characters to expose the search with a preset filter, on a workspace level. It would make mentioning entities easier.
Different solution to the same problem: Hotkey for Actions Button & Database Selection During Entity Search
I would definitely vote for this if I had the votes!
I had tried to set something like this up with AutoHotKey at least for creating a new entity. It works most of the time but sometimes the key sequence gets messed up because of delay on the UI where the pauses in between simulated keystrokes are insufficient.
I also think it is really overdue for search (both global and in-line) to be able to search fields other than rich text and allow you to apply some filters. Once you are able to set a bunch of filters and search other fields, then I think your suggestion of custom shortcuts/strings to insert particular references can be even more powerful because you will be able to get very specific.
I also think this is an area where I think AI could/should provide users with help by analyzing context (not only the text being typed, but also other entity fields) and ensure the top hits as you search for entities are most relevant to the context (sort of an advanced autocomplete). That could truly enhance the writing experience.