So the project or release or iteration is done. We’ve “finished”. The customer and users are (hopefully) reasonably satisfied, and we say that we’ve delivered the software.
There’s a second hidden deliverable that we don’t usually think about and that’s the malleability of the thing we’ve just delivered. How easy it will be to modify the software in the future.
We can think of it as the “potential cost of future change”.
Even though we cannot measure productivity and estimating this future cost is likely to be either impossible, pointless, or both; it still may be a useful concept.
Once we start to treat the potential cost of future change as a deliverable in its own right, we can have important conversations with the team/customer/user. We can trade off the potential cost for future change against getting the next thing released as soon as possible.