I think Keisha will overtake Chelsea, if she is able to. This will depend on the availability of large enough implants. Keisha's dedication to being huge is one of the many reasons we love the lady here at the BEA.
Chelsea has already taken her place in the Pantheon of all-time greats. If she is ever surpassed in size by Keisha, or indeed anyone else, it will not diminish her status.
Pix