Your hypothesis that those suffering from split-brain syndrome
could potentially read the bass and treble clef lines independently and thus process the lines independently. Perhaps this advantage would be meaningless at the professional level, but it surely could have the potential to make it easier for beginner pianists.
is flawed. That is because communication between the two brain hemispheres is required in order to learn to play the piano.
Encyclopaedia Britannica points out that
Split-brain syndrome, also called callosal disconnection syndrome, [is a] condition characterized by a cluster of neurological abnormalities arising from the partial or complete severing or lesioning of the corpus callosum, the bundle of nerves that connects the right and left hemispheres of the brain.
The primary cause of split-brain syndrome is intentional severing of the corpus callosum, partially or completely, through a surgical procedure known as corpus callosotomy. Rarely performed in the 21st century (having been replaced largely by drug treatments and other procedures), this operation is reserved as a last measure of treatment for extreme and uncontrollable forms of epilepsy in which violent seizures spread from one side of the brain to the other.
With regard to playing a piano with the corpus callosum completely severed,
Encyclopaedia Britannica also points out that (emphasis mine)
Many patients with split-brain syndrome retain intact memory and social skills. Split-brain patients also maintain motor skills that were learned before the onset of their condition and require both sides of the body; examples include walking, swimming, and biking. They can also learn new tasks that involve either parallel or mirrored movements of their fingers or hands. They cannot, however, learn to perform new tasks that require interdependent movement of each hand, such as learning to play the piano, where both hands must work together to produce the desired music.
So therefore, beginner pianists will not be able gain any more abilities with playing the piano, and pianists will not be able to learn any new pieces of music as it will involve learning how to coordinate each hand with the notes within the piece.
The anterior half of the corpus callosum is significantly larger in musicians (Schlaug, et al. 1995), @AliceD points out in the excellent answer to Unilateral vision in split brain subjects
- The corpus callosum is not necessary for low-level visual processing;
- Both eyes project to both hemispheres; the left visual hemifield of both eyes is projected to the left hemisphere, the right hemifield to the right.
and Chappell (1999) also points out that;
It is argued that in terms of brain usage, technical skills and note-reading are based largely in the left-hemisphere, while the less used skills of improvisation, memorisation and internalisation are based in the right-hemisphere.
Chappell, S. (1999). Developing the complete pianist: A study of the importance of a whole-brain approach to piano teaching. British Journal of Music Education, 16(3), 253-262. https://doi.org/10.1017/S0265051799000340
Sand, R. (n.d.). Split-brain syndrome: Pathology Encyclopaedia Britannica https://www.britannica.com/science/split-brain-syndrome
Schlaug, G., Jäncke, L., Huang, Y., Staiger, J. F., & Steinmetz, H. (1995). Increased corpus callosum size in musicians. Neuropsychologia, 33(8), 1047-1055. https://doi.org/10.1016/0028-3932(95)00045-5