Not sure rumours is the right word there: a 3-car fleet was part of the original published plan at the start of the franchise (though removal of cabs was never confirmed) which included the two orphaned cars from 212 and 217*. The "rumour" I've heard is that this plan has been quietly shelved since.
This is the answer i got of a fellow group member on the northern railway connect group;
There was the original intention to form 3 car sets by inserting a 150/2 car inside a 150/1.
These are still required to replace 150 + 153 combos, so the 153’s can go off lease.
I think this has not been done yet due to the units are still required as 2 car, but as the new units come into service, and release the requirements for this then it’s possible this will still happen.
It may also be the reason the angel ones haven’t been sent for refurb recently, as there was ‘rumours’ circulating, that the units to be used as centre cars, were to have the driving cabs removed on refurb to increase passenger space.
