right now the fate of E_STRICT error messages is uncertain. A few
people think those should change to fatal after a reasonable amount of
time, is two years (e.g. 5.0.0) reasonable. A few even think a minor
version like 5.1 to 5.2 is enough but the majortiy (at least i guess
so) wants the change only on a major version change like 5.0 to 6.0.
I'd back the majority over this. Changes from E_STRICT to fatal in minor versions is out of the question; most people still use PHP 4.3.*, and this is something you're failing to consider here.
So that'd be a major version bump for them. :)