If A/D is on chip or on board, does that make a difference for the end user? (I don't know)
The primary difference between CCDs and active pixel CMOS sensors is not where the A/D is done: Canon for example still uses off-board ADC, like all CCD cameras do.
Instead most basic difference is that an active pixel CMOS sensor reads out each photosite by transferring the signal directly to the edge of the sensor, and amplifying it in the process, which helps to reduce the effect of subsequent noise in the analog electronic signal path. I see no good reason why anyone remains nostalgic for the older, slower, noisier, unamplified approach of a CCD. In particular, Ronald's idea of a CCD with on-chip ADC might be viable, but it would not address the primary disadvantage of CCD's.
On the other hand, most recent active pixel sensor designs [Sony EXMOR, recent Panasonic 4/3" sensors, the Aptina sensors in Nikon One cameras, the CMOSIS sensor of the newest Leica M, etc.] also then do the ADC on the sensor, and in fact do it with an ADC unit at the end of each column of photosites, and this early ADC seems to help further with noise reduction, by avoiding the need for the analog signal to be transferred along the sensor's edge and beyond.
CCDs might be better suited to small volume products: apparently, once a basic CDD photosite is designed, it is relatively easy to lay out sensors of various shapes and sizes using that photosite design, whereas each different shape and size of active pixel CMOS sensor requires more new design work.