This sequence of events can give some light on the issue (quoted from 4chan):
Oct 20th/21st: Wikileaks tweets 5 tweets with misspelled words. The incorrect letters spell "HELP HIM". The Wikileaks twitter has never made a spelling error, let alone 5 in two days. [1]
Oct 21st: Massive DDoS attack on US internet. Wikileaks tweets to imply the attack originates from its supporters, asking them to stop, no evidence supports claim.
Oct 21st: London Airport evacuated due to "chemical attack", potentially used as cover to fly Assange out of country.
Oct 22nd: Gavin MacFadyen (mentor to Assange and key player in Wikileaks) dies of lung cancer.
Oct 23rd: Wikileaks Tweets poll asking how best to prove Assange is alive (he still hasn't appeared on video or at the window since).
Oct 24th: Wikileaks Tweets video of Assange and Michael Moore recorded in June.
Oct 26th: 4chan users successfully successfully decode their first message in Wikileak's blockchain. Threads are instantly flooded by shills saying that it's not worth looking into. The blockchain is blocked with fees and 43000 unconfirmed transactions appear in the mempool.
Nov 6th: Huge DDoS takes down Wikileaks for first time in years.
Nov 7th: Various entities notice hundreds of Podesta and DNC emails are missing from recent leaks, accessed with direct entry.
Nov 8th: Trump wins.
Nov 12th: Assange meets with Swedish prosecutor regarding rape allegations, lawyers barred from attending, meeting conducted via an Equadorian ambassador (not face to face)
Nov 14th: Wikileaks releases insurance files, SHA-256 hashes do not match those tweeted in October.
> Oct 21st: London Airport evacuated due to "chemical attack", potentially used as cover to fly Assange out of country.
Cover for who to fly Assange out of the country?
When an airport is evacuated that's going to stop air traffic out of the airport, and it is likely to cause enhanced scrutiny of the people who are at the airport. If the people trying to get him out are not working with the UK government, that would not be the opposite of what they want.
If it was the UK government trying to get him out, they could probably arrange for a special flight to leave the airport while it is ostensibly down. Of course, that would draw attention to that flight because you'd have assorted airport workers see that a flight had received special permission to leave a closed airport, and so it must be something very important.
Why would they do that, when if it is the UK government they could simply take Assange in a windowless van to a UK military base and fly him out on a military flight? That could easily be done in a way that would have virtually no risk whatsoever of calling attention to the operation.
Actually, the same goes for anyone else trying to get him out. The hard part in moving Assange is at the Ecuador embassy end of things, not at the transport out of the UK end. If the Ecuador embassy is cooperating with the move, then the windowless van works no matter who the party is.
Furthermore, in addition to the practical aspects you list, it was actually London City Airport that was evacuated; that's the small, single-runway one in the Docklands.
Because of its steep approach there are only certain specified aircraft types permitted to operate there and anything untoward would be quickly spotted.
It's also 11 miles east of the Ecuadorian embassy, requiring a journey right through the heart of the city. Whereas RAF Northolt is a much quicker and easier trip to the north-west...
I think we see here how 'false news' starts. Unhelpful facts are omitted or made ambiguous, and then mixed with a spoonful of conjecture.
Also jets leaving an airport aren't invisible and anyone living near there could have noticed a plane leaving an airport that was supposed to be closed due to a chemical attack.
It would actually be pretty counterproductive to draw so much attention to the airport and then send a supposedly secret flight out of it.
Oct 20th/21st: Wikileaks tweets 5 tweets with misspelled words. The incorrect letters spell "HELP HIM". The Wikileaks twitter has never made a spelling error, let alone 5 in two days. [1]
Oct 21st: Massive DDoS attack on US internet. Wikileaks tweets to imply the attack originates from its supporters, asking them to stop, no evidence supports claim.
Oct 21st: London Airport evacuated due to "chemical attack", potentially used as cover to fly Assange out of country.
Oct 22nd: Gavin MacFadyen (mentor to Assange and key player in Wikileaks) dies of lung cancer.
Oct 23rd: Wikileaks Tweets poll asking how best to prove Assange is alive (he still hasn't appeared on video or at the window since).
Oct 24th: Wikileaks Tweets video of Assange and Michael Moore recorded in June.
Oct 26th: 4chan users successfully successfully decode their first message in Wikileak's blockchain. Threads are instantly flooded by shills saying that it's not worth looking into. The blockchain is blocked with fees and 43000 unconfirmed transactions appear in the mempool.
Nov 6th: Huge DDoS takes down Wikileaks for first time in years.
Nov 7th: Various entities notice hundreds of Podesta and DNC emails are missing from recent leaks, accessed with direct entry.
Nov 8th: Trump wins.
Nov 12th: Assange meets with Swedish prosecutor regarding rape allegations, lawyers barred from attending, meeting conducted via an Equadorian ambassador (not face to face)
Nov 14th: Wikileaks releases insurance files, SHA-256 hashes do not match those tweeted in October.
[1]: http://img.pr0gramm.com/2016/11/17/a4af28fa5ce1c059.png