Given that diesel rolling stock is in short supply and Pacers are due to be withdrawn, plus uncertainty as to if replacement rolling stock will fill the gap, why would 153's be scrapped? Are they life-expired beyond repair or is there going to be an injection of available rolling stock with the Flex trains and IEP units?
The 153's could easily be incorporated into other units such as 150's to avoid disability alterations, however I suspect that no one wants to cough up the leasing/track access charges.