1. Not necessarily - 4 short people behind 4 tall people will do the job. But I would argue London platforms ARE overcrowded already, rather often. Mostly because you can only control where people go a certain amount. If everyone gets off many trains at the same stop, but don't leave, there isn't much TfL can do short of asking people to leave for their own safety. Maybe if TfL actually got any decent amount of funding (Like Southern and SouthEastern got due to being rubbish) from the government, they could work on creating further lines and spaces that would decrease Underground congestion. Instead, the government has cut funds and the Mayor has frozen fares. And yet people still want infrastructure to improve.
2. 1 Person != 1 Wifi, but if 1W = 0.2P, you can still get a good estimate.
3. TfL is a large bargaining chip for the mayor - no mayor would even consider risking a PR disaster like the one that could come from this.