Another metric I go by is there is no one on team have overlapping knowledge of the code base. In other words, no other teammate is suited to review your code because they have no context of it.
I think a decent definition is "software where no one person has the whole system in her head", i.e. where reading existing code takes as least as much time as writing code, and any change may have unforeseen ramifications on the system as a whole.
As a Googler working on a single-developer project / codebase, I'm sorry to hear that you didn't get traction. Very grateful for my mostly autonomous role :) There are tradeoffs of course, but to me the reduced overhead of no meetings and greater creative control are worth the trouble of an increased workload and providing support.