If a customer can afford an 8x8 HDMI matrix a basic control system from Elan, C4, URC or RTI doesn't seem like too much of a stretch. If your customers already have tablets and don't mind using them in lieu of remotes (I don't personally recommend this for frequently used rooms) the cost of the control system should be well below the cost of the matrix.

Regardless of what you use, the customer still needs to be able to easily choose the matrix routing they require, and control their cable box (and up to 5 additional sources) so you will need some sort of universal remote solution. AT LEAST use a base station that allows IR port routing (MRF-350, ProLink.r) but seriously consider stepping up to a real whole home system, and not stretching a single room solution to "make it work."