The industry has been touting MSIX as the replacement for the AppX and MSI packaging formats ever since its announcement in 2018. MSIX presents us with a new application packaging format for both the traditional and modern managed workplace environments. It is an improvement of the AppX format adding support for win32 apps to give us a single application package that can now be distributed via MDM, ConfigMgr and the Windows Store. MSIX facilitates easy application upgrades with optimized packages, providing enhanced security, sand boxing and network and disk utilization improvements.
Microsoft have provided the MSIX Packaging Tool that can be used to convert any win32 package. The tools currently provides good results with an example of a gap being around MSI custom actions. This is supported from Windows 10 1809 onward. Third party vendors such as Flexera also having support for MSIX packaging.
It still is early days with the MSIX format, it is still remains to be seen if this will become the new packaging standard that creates one application deliverable. Early testing does look promising. One of the limiting factors of the Windows Store has been not allowing Win32 apps and this will certainly remedy this. The adaption will be driven by adaption within the industry in general, especially from the major application vendors, this will influence MSIX as the replacement for AppX and MSI. So in short MSIX is not ready yet but maybe soon.