I agree with the first part ("current Sentry isn't Open Source"), not with the second one ("unless there's an actual community"). A software can be Open Source without actual development community.
Ah, wait -- you don't say that Open Source requires a community. You state that, if there was interest in the older version of Sentry, then that version could be considered as Open Source. I agree with this one as well, then.
[I considered deleting this comment, but maybe it will be useful to others who have not read closely.]
Right, exactly. I'm not saying a project must have a community in order to be Open Source. I'm saying in order to be considered for a list like this, something should be a project in its own right rather than just a stale version of another project.
Ah, wait -- you don't say that Open Source requires a community. You state that, if there was interest in the older version of Sentry, then that version could be considered as Open Source. I agree with this one as well, then.
[I considered deleting this comment, but maybe it will be useful to others who have not read closely.]