No, they won't make any real attempt to slow down. No, they won't do more than make incremental advances. To the extent that large benchmark gains occur, they will be shown to have little practical value.
If it'll come to pass, we'll probably have a groundbreaking discovery that the brain violates the physical Church-Turing thesis on our hands. That would be quite unexpected.
Maybe if it's a deliberate decision by the researchers. A path to more capabilities is rather clear (recurrence and explicit memory).