In the patent, Apple talks about how physical buttons that depress could potentially act as another ingress point for water, and as such, they have designed what could potentially be a fix for that problem.
According to the patent’s description, “The engagement components may extend distally from the button, such that a portion of the engagement components may be positioned within apertures formed in the sidewall of the housing. The assembly may also include a plurality of supports, a tactile dome in contact with the button and at least one of the plurality of supports. A sensing component of the assembly may be positioned adjacent the housing and in alignment with the button and/or tactile dome for sensing actuation of the button within the assembly.”
That being said, there’s no telling if Apple has plans to eventually makes this patent a reality, but hopefully they do as iPhones with a greater degree of waterproofing sounds like a great idea.