An observation with the planned Terminal extension, this was the first impression released publicly:
https://www.stanstedairport.com/abou...l-development/
Here you can see the Skylinks that replace the TTS run along the full length of the rear Terminal extension.
https://www.pascalls.work/stansted
If you look at the video in the Pascall+Watson design however this is not the case, with instead the SAT 3 link direcly linked to the north end of the building and the SAT 2 link instead linking to the bussing terminal.
I believe, looking through the lines, this is so the Skylinks and Bussing Terminal can be more easily put in situ first, allowing the TTS decommissioning before the "three-bay" extension can be added to the rear. That also could be a logical reason for relocating immigration to a lower level, so that can happen before the "three-bay" extension above it. It's worth noting it's actually only a 'two-bay" extension in terms of the roof structure, as one is already existing as the rear canopy above the TTS tracks. But it will deliver a "three-bay" extension in terms of floor space as the interior area will reach all the way to the edge of the structure, similarly to how it does to each of the two sides. They'll need to be some TLC though the existing rear canopy as it's filthy and rusting like you wouldn't believe and something will have to be done with SAT 2 internally to make it fully split level throughout with the new domestic arrivals facility to the north of the main Terminal.
My understanding's also the shoreline check-in may happen earlier rather than later during the phasing. I believe it actually results in a slight reduction of desks, however around 30-40% of current desks in the zoned check-in cannot be used simultaneously due to queueing space. Further efficiencies could also be created by more self-service bag-drop with more common-user desks and pooled resource.
Another area of interest is the space immediately behind security before you wrap round into duty-free. Once the domestic arrivals corridor which runs along-side that is removed, should give more space for post-security re-packing/orientation.