@infinite.loop wrote in a post somewhere that he did not want breaking changes going into 1.5 if we can avoid it.
According the train model "rules" we did craft we aren't allowed to break the same subsystem combatibility twice in a row. Depending what 1.4.0 did break we shouldn't break all again in 1.5.0. If there is only one sub system (like music) we did break with 1.4.0 then I would still allow the 1.5.0 to break (like music) compatibility again to get the refactoring done for 1.5.0, in other cases next stop would be 1.6.0.