London will still be the centre of English-speaking Europe. It's the biggest irony of brexit: London is vehemently opposed to it, but likely not going to be all that affected by it.
Dunno, most people I know are trying to escape London, miserable weather, low pay, massive increase in rent, uncertain future. Despite having most AI startups after US. At FB London as a SWEng you are capped at most at 110k; in the US you'd earn 4-5x more for the same job and on more interesting projects as well.
Further anecdote to support that claim: in my old job an admin who worked in the London office for over seven years, and had numerous raises and promotions in that time, was on the same salary as her newly hired graduate counterpart in the states. Relatively rural area in the states too, it wasn't NYC where the cost of living may have made that acceptable.
Our relative salaries with the states are god awful.
I worked for Facebook London office and the pay level compared to our US counterpart was something that my more talented peers were talking about. The idea of a ‘cap’ feels alien to Facebook in general, but I can confirm that to get more than that, you would probably have to be an exceptional developper -- think: get recognised at a conference, have your work #1 on HN for 24 hours, have regular conversations with iOS or Android core devs, etc.
I joined at the same time as one guy who was working remotely full time, officially based in London. But he was the co-founder and the lead developper of the most used technology at Facebook, so…