In my earlier post, I should've included the following info as part of the rationale for us including @ids in all references:
We very likely will not be changing our "best practice" of including topic ids, even though (as Radu states) omitting topic ids in a reference makes it easier for authors to change @id values in the future. That's true. However, the business value of that freedom is tiny IMO.
The DITA spec says including the ID is optional. Because it's optional, it appears to be up to tool vendors whether the presence of an id is required. Over the years, we've run into several instances where not having an id causes errors--the tool vendor in those instances apparently says the ID is required.
If you stay fixed to just one vendor, I suppose a business rule of omitting topic ids would be fine. But, it you want to remain somewhat independent of a single vendor, my recommendation is to always include the topic id, even though the spec says it's optional.
My two cents.
At any rate, giving us the freedom to add a topic id is greatly appreciated.