If anyone killed Flash and Java, it was Apple by refusing to support either on the iPhone. All the users did was make popular a platform that didn't support them. If Apple had supported Flash and Java we probably would still have them.
Signed code that users had to install was tried before with ActiveX. It didn't work either because you can't rely on random developers to write secure code either. It's also how IE ended up with Flash. Click here to download Flash (signed by Macromedia).
So basically everything sucks because we're human and make mistakes. Maybe one day we'll have machines that reason more thoroughly than us and they can come up with a secure platform. Until then... Javascript and sandboxes.
Apple may have put the nail in the coffin, but long before that quite a few developers and users were avoiding Java programs when there were alternatives, and ClickToFlash was a popular browser plug-in. As they often do, Apple saw which way the wind was blowing.
Not paying attention to the news? Just wait until WebAssembly gets more mature.
Flash and Java Applets may not be "dead" forever, but they also are not likely to ever be more than undead zombies.
You seem to be talking about new platforms that may derive some part from the old. I'm not saying WebAssembly won't be used for new platforms as that's sort of the whole point of it.
What I'm saying is that WebAssembly won't bring back people making Flash .swfs or writing classes derived from java.applet.Applet in any mainstream way. In that sense Flash and Java Applets are dead. Maybe someone will hack something together that allows you to run them, but that won't bring the developers back to the old platforms.
If Oracle or Adobe announce something, maybe the industry will jump on board, but currently I don't see anything in your list that makes me change my mind about Flash and Java Applets being dead and not coming back.
As3-WebAssembly is a compiler for porting Action Script 3, Flash's programming language, into WebAssembly. Already integrated into Flash Develop.
Microsoft and Xamarin efforts to port Mono into WebAssembly, will allow making Silverlight apps again.
You are free to believe this won't turn out into anything, I rather think we will end up in WebAssembly + Canvas/WebGL in a couple of years.
The new platforms may use the old languages, but the runtime libraries are not the same. The new platforms have different APIs and functionalities (no threads in TeaVM for instance).
To simplify my point. ActionScript is just a language. Adobe Flash was much more than that. Maybe companies really will find some compelling reason to start using ActionScript again... but Adobe Flash and it's SWFs will still be dead.
Not yet. If "WebAssembly" is anything like actual machine code, then it will be easy to compile a bunch of languages to "WebAssembly," and a huge pain to make them talk to each other. So nothing really changes.
While I am mostly a pessimist, this is one place where I harbor a tiny sliver of optimism. Once users recognize that something is awful, and have the means to get rid of it, they eventually do so. Client side Java and Flash are dead, because everyday users figured out that they sucked, and were given the option not to use them. We're getting close to a situation where average people recognize that millisecond auctions to run arbitrary code on their machines are a bad idea, and those people also have the tools to say "no." Hope springs internal...