I just finished a simple proof of concept test.
It works. It is definitly possible to control a switch matrix with 2 4051's so you can simulate any key in an 8 by 8 key matrix being pressed.
I can't say that this will work with any keymatrix, but for my toy with a 6 by 7 matrix it works.
This is a simple toy (Vtech Little smart alphabet desktop) with a simple matrix without diodes on the rows / coloumns.
I will post more info later.
MikMo