We are at an interesting cross roads. IE11's usage globally has understandably declined and the Windows 7, the last operating system to use IE11 as it's default browser, is officially no longer supported by Microsoft. Microsoft's own applications, such as Teams and Office 365, will officially no longer support IE11 by August 2021. That said, IE11 is not "dead" yet. Windows 7 has extended support for Enterprise customers. IE11 is also installed on Window 10 for compatability reasons. As long as there are Windows 10 machines, IE11 will still be an available browser for customers to use.
As stated earlier IE11, once the dominate force on the internet, has around 1 to 3 percent global usage, depending on how you measure. Unfortunately, among enterprise users, this usage is much higher. Ultimately, the decision how or if to support IE11 is totally dependant on your situation. Support also does not mean that you have to provide the same experience. One can provide an experience using modern CSS, while providing fall back layouts for older browsers that don't support the latest and greatest.
The obvious question is does Bedrock Layout Primitives support IE11? An earlier version of our components did attempt to provide fallbacks for IE11 while supporting modern layouts. It was later discovered that several of the fallbacks were incorrectly implemented. At that point we had two decisions: go back and fix them or rip them out and focus on modern evergreen browsers.
Ultimately, we decided it would be best to rip out all the fallbacks for IE11. We decided to do this for a few reasons. The library was still young enough that it would not cause large cascading impact on people's apps. Providing fallbacks are not the job of the library, because only you as the app developer can know what is the most appropriate fallback for your application. Any fallback that we provide would then have to be overridden creating a bigger problem for you the developer.
Going forward, Bedrock Layout Primitives will support the latest and greatest in CSS layouts while providing fallbacks for all the 4 major browsers latest version minus one version.