Custom column after filtering

I'm using Metabase, linked to a MongoDB database.
I created a quite simple question with the visual editor, that contains the following steps:

  • add custom column, using a custom expression
  • filter on another column
  • count records grouped by the custom column previously added

It seems that it's not possible to add the custom column after the filtering step. However, imagine that the collection contains 1 million records, and after the filtering, we have only 1000 records. Wouldn't it be more performant to add the custom column only on 1000 records rather than on 1M records ?

Adding the custom column AFTER the filtering could be done if I translate the question into native query (indeed, I could first do a "match" step, and then an "addFields" step, and the final result would be the same. So I'm wondering why this is not possible to do with the visual editor. Is this planned ?