Infinity Ward thinks in issues based on the numbers. If they see that shield combo is centralized only in two game modes out of the many others, they won't consider it worthy enough for a patch. Think about why quickscoping wasn't gimped. Joe Cecot said that the "minority" are good at it, resulting in the sniper's balance being off-set as a result.
I really hope they patch the shield + C4 combo, but I hightly doubt they will...
~RUGGED SAVIOR