peak detector as voltage lock

Hi. Having this idea buzzing around in my head - I got to ask for it.

I've seen schematics of AD converters using counter to make a reference voltage. Those are also equiped with a holding circuit consisting of a capasitor and a small fet/jfet.

Question is: Will or could it work to use a peak detector instead of a regular fet/cap holding circuit?
That is using a peak detector as a holding circuit.

Any disadvantages exept for increased number of components doing the same?