FWIW, having a TODO file is mandatory for anything in staging/, see Documentation/process/2.Process.rst.
https://www.kernel.org/doc/html/latest/process/2.Process.htm...
Moreover TODOs are added for unmaintained drivers outside of staging/ in order to prepare for their relegation to staging, e.g. see commit a0d58937404f ("PCI: hotplug: Document TODOs").