Hi Vicke -
To be clear, POET has not failed the identified plugin. We haven't even officially reviewed it. I'm guessing you are dealing with one of the member organizations who is using the same process.
The reason a plugin would fail if it cannot be uninstalled (in my opinion) would be because it is not meeting the minimum requirements of a Moodle plugin. And if it can't uninstall, it is likely throwing an error.
In the case of the 3.0 plugin, it is because of the circular dependency, and the fact that Moodle core won't allow the uninstall. I'm not sure how that would be resolved easily, so I would suggest that if everything else is fine, that should not prevent you from using it. The circular dependency issue is something that has to be worked out with core Moodle to resolve.
mike