EM should only install extensions compatible with current TYPO3-Version
When the EM fetches the "latest extension version" it should also consider the typo3 dependency constrain so that only extension versions compatible with the current TYPO3 version are considered.
This goes in line with the TER cleanup initiative
It would also allow extension authors to provide extension versions for different TYPO3 releases.
Some issues / conflicts could still arise with this, like:
Extension A compatible with TYPO3 6.2 depends on Extension B which does not have a TYPO3 6.2 compatible version (yet).
So maybe there should still be "some way" to overrule this compatibility check in cases where the admin is sure of what he's doing.