As much as I love the PCE, and as much as I'm sure the design made a great deal of sense back when it was designed, technically and financially, I can't help but feel as if the entire system suffers from a preponderance of missed opportunities, so many of them minor.
An extra background layer, more CPU work RAM, lack of BG tile flipping, even an additional audio channel or two or a separate sound CPU to take some of the load off the main CPU. And yet, compared to its contemporaries, it was a much more robust design. Technology was, as it is now, changing rapidly, so there's no way of prognosticating what effect even the most minor of changes would have had on system cost or longevity.