It would be nice to have an easy way to to add custom extensions to the source-tree to deploy them for validation of plugins or hosts using those extensions.

Perhaps even offer a staging folder them upstream (open to pull-requests).

e.g. https://github.com/x42/lv2/ deploys ardour.org extensions when configured with ./waf configure --unofficial -- However that no longer works with the updated built-system in LV2 1.16 that hard-codes the spec-map.