Because this time around we will have instant (no install) apps that are inherently sandboxed? Seems like a pretty big win to me.
I think win is having free software or at least opensource apps that are trusted by distributors and easy to analyze/modify, and actually own (meaning have on your harddrive and fully control). And we already have that win.
There's a big difference between an imperative (e.g. arbitrary code) and declarative installation process. Imperative installation is most common on Windows due to the initial decisions made by the registry designers + the Windows Installer originating from Office and starting with imperative. Declarative installs are common on the Mac where "installation" usually means dragging a binary from the DMG to your Applications folder. OS X then manages OS integrations declared in an app manifiest.
Declarative installations delegate to a system which has a broader view and standard mechanisms to handle state transitions required for installs, upgrades, and uninstalls. Imperative installations frequently leave residue and are hard for even Windows to fix. I spent years of research and have several patents on trying to figure out how to distinguish between "extension points" of the OS and private state to create a sandbox with the necessary pinholes. Even with those tools handy, many software shops see no reason to upgrade because the Windows end user accepts a life of installers.
I see logic in starting from scratch. This time we can create an end user expectation of declarative and (laterally + vertically) sandboxed apps. Hell, that's what we tried to do with Windows 8, but it was unfortunately restricted to the "modern" (aka full screen) apps that never caught on.
It's still sandboxed, and limited, so what's cached this way is perhaps easy to totally remove by the browser. But that's not because of the declarativeness, but because of sandboxing.
sure, linux is doing that much better, but until we get linux (homebrew for windows?) installers for windows, i'll prefer webassembly, at least for casual use.
I was involved with Java applets when Java was in beta and one of the most annoying things was that JDK 1.0 did not come with serialization.
I would build applets that displayed content generated on the server and serialization-deserialization code could be 2/3 of the program. Most people had a slow net back then, so the download performance was a big deal.
JDK 1.1 put serialization in right away, but Netscape had already introduced it's own incompatible serializer, and there were delays in getting JDK 1.1, plus people didn't like Java serialization -- practically there was a year or two where you couldn't use it.
Applets had enough teething pains that people quickly came to the conclusion that they weren't worth the trouble, then Flash came along which came closer to what people wanted at the time.
Especially since so much of the internet was once on Flash and we're looking at the loss of historical archives.