The extra changes proposed by al13n would potentially cause more problems than they solve.
Note that generally backports are supposed to be leaf packages (with some exceptions), so that the scenario given should rarely occur, if backport policies (other than this proposed change) are correctly applied.
It is much better to be first discussed on the mailing list.
I agree with tmb, stormi, and sander.
The extra changes proposed by al13n would potentially cause more problems than they solve.
Note that generally backports are supposed to be leaf packages (with some exceptions), so that the scenario given should rarely occur, if backport policies (other than this proposed change) are correctly applied.
It is much better to be first discussed on the mailing list.