I have a code system (Compendium of Physical Activity) where a property of each code is a Quantity. Observations of different physical activities, for different durations, can be compared using the Quantity property of the observation code when the code is selected from the compendium.

So,'Quantity' added to CodeSystem.property.type

And valueQuantity added to CodeSystem.concept.property.value[x]

However, that leave properties of 'integer' and 'Quantity' and nothing in between. So it may make sense to add 'decimal' and 'valueDecimal' at the same time.