EM should inform admin if a local extension is outdated and needs an updated extension
This issue is more related to system extension as to others.
Imagine a site was running TYPO3 4.0.1 for several month and e.g. the RTEhtmlarea was installed locally from TER (with security patches, etc.). Now the admin decides to update to TYPO3 4.1.0. The RTEhtml will not work anymore, because the local installation of this extension (made for TYPO3 4.0.x) is not compatible to TYPO3 4.1.0 anymore.
The Extension Manager (perhaps additionally the update wizard of the install tool) should inform the admin, that the newer system extension is required and that he has to uninstall his local extension.
Just read bug-id #17082 to see what could happen.
(issue imported from #M5178)