A few months ago I think someone posted that MAN had applied for planning permission to expand the current T3 security area in order to accommodate the new scanners. Well it seems that isn't happening now:
from Manchester Airport Consultative Committee – Friday 26th April 2024, reported on forums4airports
Consent was secured for a replacement security search facility for T3 in September 2023 that would have involved building out over an existing area of apron (resulting in the loss of 1 aircraft stand). However, it has been decided not to progress with this scheme and the application that MAG submitted to vary conditions attached to the planning permission to allow for design revisions has been withdrawn. Further master planning options are being considered for the works to accommodate the DfT security search upgrades, along with opportunities to remove the current circulation constraints of T3, and improvements to the departure lounge.