Unfortunately, as with all previous FRIs, there has to be a cut off date. It's just plain bad luck for those on the wrong side of the OCU+7 / 1st April.
I agree with Leon and others that this is a pretty good deal overall which should hopefully drag more people through from end of Initial Training ROS to their EDP.
Word of warning on the £70k Retention Payment and tax implications... This payment, when added to usual salary, will see individuals break the £100k barrier in a single tax year which will lead to loss of some or all of your tax free allowance. Hence a further tax bill could be due in the year following receipt of payment. Those who took earlier FRIs will probably already know this. Some sound financial advice (Al R?) can reap rewards as there are ways to reduce your effective income below the £100k barrier and save on tax (small contribution to a personal pension for example...).