Hence, why the referenced thread was moved to the Feature Requests category, and is really "unsolved" until such a feature is implemented. (I asked the OP to remove the solution he gave me.)
This thread's caption should be edited to reflect your "auto layer tag" feature suggestion.
But it is definitions that are tagged ?
And definitions only "use" a layer as a default to render the instance attached to the cursor, when in "Color by Layer" mode. Once inserted the instance reverts to rendering in the active layer's color, as it is inserted to "use" that layer. (In any other rendering mode, the definition's layer property has no effect, AFAIK.)
Can you be more specific in how you envision this to work ?