Bit of a strange announcement. This already happened a long time ago. The MSIX engine that they mention uses a lot of the same technology as Windows Update and thus has many of the same features. I suspect what they mean is adding some more APIs to try and help non-Chrome non-MSIX apps benefit from those.
MSIX is an interesting beast. My company sells a tool called Conveyor [1] that can create these packages from any platform including macOS and Linux given a simple config file for apps using runtimes like Electron, Flutter or the JVM (it's free for open source projects). We do a lot of work to make MSIX work better and be easier to use, because out of the box it's quite raw and in particular there are a lot of bugs in Windows 10 that Microsoft never fix because they view it as EOL. Conveyor creates a tiny 500kb installer EXE that drives the MSIX package manager API to do the install whilst working around these bugs.
Amongst other things, MSIX gives you:
• Chrome-style silent background updates on a regular schedule, even if the app isn't running.
• Incremental block-based delta updates.
• Incremental block-based downloads and installs, i.e. Windows can re-use parts of one app to install another, based on file block hashes. Makes installs very fast when they share a common runtime!
• And those installs/updates can pull blocks from other machines on the LAN too!
• Declarative installs and OS-controlled uninstalls. Writes to the user's AppData directory are virtualized, so uninstalls can be clean.
• Packages can be installed without admin rights, without dumping stuff in the user's home directory. Windows runs an elevated service that does the install for you.
• You can sandbox apps if they're shipped with MSIX.
• EXEs can be automatically added to the user's path, without needing any terminals or shells to be restarted. MacOS can't do that!
• Windows admins can easily deploy and manage them.
• They're cryptographically signed and their integrity is protected by the OS, so malware can't fiddle with the binaries (unless it manages to elevate to root).
• Although you can't create them with a regular zip tool, you can extract them with one.
Conveyor adds some other features on top like the ability to have web-style "update immediately on launch" updates, and a simple Electron/JVM control API so you can force updates on users.
It's a pretty nice feature set overall and has some big advantages over Squirrel, which is what Electron uses. However, I would definitely NOT recommend you try and work with MSIX directly. Microsoft's tooling is quite awkward, and their policy of only supporting fully up to date Win11 machines - and only from Windows - means you can't realistically distribute apps using MSIX unless you go via an intermediary like Conveyor that's committed to making it work. You'll just hit lots of weird bugs and installs that fail for no obvious reason with mysterious error codes. We ploughed through the pain so you don't have to.
As much as anything it seems like a potential rebrand from "Store Updates" to "Windows Updates" and a further merging of the UI of the two similar but related systems. That seems like a good idea to centralize all of that UX together.