Having now read most of the proposal document I think that they have been quite creative in their plan to bring the back up run way into use as a step towards the eventual full second runway.
i know of no other airport that has the same number of go arounds as LGW and requires all involved to be on the ball from flying very accurate approach speeds to timely clearing the runway and being ready to roll immediately.
Given that the bulk of traffic volume flys south from LGW and that by using the back up runway would free capacity for the traffic heading in to west Europe & Scandinavia, having said that it will be a huge engineering project just to add concrete to the north of the main runway because of the need to move Juliet taxy way which have to go the north of the ponds and the fire training area will need to be relocated to allow construction of the bypass loop around the runway heads.
By making it only available for take off negates the need for approach aids and associated lighting, it will of course cause even more problems in LVP’s due the higher volume, but its only a couple of days a year that it hangs around all day ( fog)
i doubt theyll actually have two aircraft raft taking off simultaneously, but having a departure whilst another aircraft is on short final will improve flow for sure and it will allow greater flexibility for wake separation, LGW is unusual in having a very mixed aircraft type from WB to super heavy and lots of narrow body types also.
my only criticism is it’s a fudge when what is really needed is a new full length Cat3, but that’s the UK when it comes to infrastructure