While the keyboard membrane probably adds a tiny amount of insulation and resulting added heat, there would be no point in running such a test, as there would be no point in buying and using a MacBook Pro without the keyboard. You might as well buy a desktop iMac. The only way to remove the membrane would be to destroy the keyboard. Nobody is going to do that.
Even if someone did this, and used a bluetooth keyboard, the removal of the keyboard membrane will not make a differential difference in throttling or heat management.