Currently, PREWHERE is not too useful for Replacing / Collapsing tables with FINAL
See #23702 #8684 #24433, etc.

At the same time one of the obvious optimizations here is very similar to PREWHERE behavior:

SELECT *
FROM replacing_mt_table FINAL
WHERE (pk_col1, pk_col2) IN
(
    SELECT
       pk_col1,
       pk_col2
    FROM replacing_mt_table
    PREWHERE non_pk_col='val'
)
AND non_pk_col='val'

I think it should be possible to make something similar to that rewrite during PREWHERE itself.
I.e. during the filtering of the non_pk_col 'expand' the matching ranges to a full (wider) range of those PK values.