A new solution has been detected...

The wide distance between the roller shafts on the Screen Block I just modelled made me realise that, with the right optical endstop and PET roller setup, I could eliminate the independent application rollers. I'm using optical endstops everywhere because they're quieter and give me the opportunity to move past the endstop if needed. My idea is to have a long strip that extends from [x axis limit] all the way to [absolute max x axis limit].

Benefits

• Removes 2 steppers, saving >£10
• Due to the removed steppers, it becomes possible to M8P + Monst8 + 2x MOT, saving around £13.
• Removes 4 100mm linear rails, saving £20.
• Allows more space for cartridges in both length and height. 
  • I may need to rethink my strategy for holding them, because I can't imagine having so many kilograms cantilevered at each cartridge is going to work out for me. The current idea is to make the 5 cartridges part of a shelving unit and it's the entire unit that a user has to remove from the printer.
• Removes 2 endstops. Probably saves pennies but those endstops are also some of the furthest away ones from the expected motherboard installation location. 
• Makes assemby easier and reduces CAD modelling.
• The PET film will have a steeper angle, further improving peeling performance. 
• Ideally, for prints where there is an adjacent screen area to move, the Screen Block will move to said area and the PET film will cleanly peel away from the part without much worry about suction forces at all.

Potential hurdles

• When the Screen Block moves away from the cartridge. there would be more slack in the PET than with the original plan. This probably won't be an issue in practice, as I can think of a few ways to resolve this.
• All material has to be applied onto the film or sucked back into the cartridge. I can imagine that this would be a similar difficulty to fine tuning the filament-end-forming script on an MMU before the filament is removed from an FDM hotend.