Rather than focusing on it being `configurable`, I view the benefit of vim-spec-runner as being its automatic detection and configuration of the spec run command. Thinking something like the following captures this:

> An efficient and intelligent spec runner for Vim. `vim-spec-runner` automatically detects the needed runner
> and will compose and execute a spec run command in any context you specify. The primary goal of 
> vim-spec-runner is that it should Just Work (TM) for most of the workflows, configurations, and apps we 
> use each day.

Not perfect, but closer to what has been in the back of my mind as we've worked on it.