Most bamboo plan configuration accepts variable definitions, like ${bamboo.some.value} to be replaced at runtime with "the-value"

This field does not. See screenshot.

This prevents full parameterization of plans that are very similar in setup. Since our project structure and tooling is 100% similar between our repos, we would have liked to be able to create a template plan, with a plan variable, and just clone that for each repo's CI needs.

This may be a bug or a feature request, depending how you perceive the problem