As Microsoft continues its work towards Windows 10 on ARM, as well as, potentially, another reboot of its phone business, the company is also taking steps to eradicate older, non-UWP apps from its platform.
One move it is using to attack older apps is by signalling the end of Silverlight support in Windows 10 Mobile. According to a tweet by Gustave M, a new dialog will begin to appear when opening Silverlight apps.
— Gustave Monce (@gus33000) June 2, 2017
It is important to note that this won't affect every old app. Silverlight apps were built for Windows Phone 8 and earlier. WinRT was used for Windows Phone 8.1 apps (although, Silverlight was still possible), and UWP for Windows 10/Windows 10 Mobile apps. An area that a few have complained about as being of particular concern due to this change is Xbox games. Classic games that were built on earlier Windows phone versions but able to run on Windows 10 Mobile will more than likely become obsolete.
As a word of caution, there is no official announcement from Microsoft regarding this change and as such, it is best to avoid jumping to conclusions until a more concrete plan of action is discovered.