Could this simply be the speed at which a system is designed?
After reaching the end of an 18 month development
effort with 15 developers, I found myself reminiscing
over the team's gradual transition from analysis/design
modeling to code. Initially, the team's core focused
on creating and reviewing class and object interaction
models. As these settled, we coded. Thus the models
were used to boot-strap individuals and small teams.
This transition to code marked a maturity in the
developer's understanding of the problem.
Perhaps DesignVelocity encompasses a measure of the
maturity of understanding of the solution -- the software
architecture -- which starts off low, picks up momentum
as the solution space takes on definition, and peaks
when the team is fully armed with understanding to
implement. It then falls away (or changes?), as
concepts, mechanisms and patterns get embedded in code.
Being able to measure this transition in both individual
and collective understandings would have been a
useful progress metric.
I have never had a project where DesignVelocity smoothly approached an asymptote. Instead, I see chaotic amounts of design over time. You'll think you have it wired, then have the insight that completely restructures the system. There is an analogous concept in biology called "punctuated evolution". Evolution is not a process of steady "progress" towards a "goal" (me). Instead, it happens in fits and spurts.