I think within 2 to 3 years WAP-4 will be extinct just like WAM-4
Reasons
1. All trains being alloted LHB rakes and LHB rakes runs only with HOG WAP-7
2....
more... Passenger trains getting converted into MEMU.
Atleast WAM-4 was scrapped because of old age but WAP-4 has a huge number of years before reaching codal life left but still they will be out of mainline service.
Any suggestions how to utilize WAP-4 in future.