What Google is telling app developers to do will make the Play Store look better
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So just what is a squircle, you might ask. It is a shape that is in between a circle and a square. It features rounded corners and straight sides, top and bottom. According to the latest Android Developers Blog, new app icons for the Google Play Store will use the squircle shape They will remain 512 x 512 in size, but transparent backgrounds will no longer be accepted. Rounded corners and drop shadows will be applied to these icons.
Starting early next month, developers can start uploading their new icons and Google will tell developers if their submissions meet the new specifications. On May 1st, any new icons must use the squircle shape, and on June 24th, original icons will be switched to the new legacy mode. The latter is a squircle shaped icon with an original circle design inside it. Doing this will allow both old and new icons to use the squircle design.

Examples of original icon, new icon in squircle, and original icon in legacy mode
So what is the reason for making this change? Google says that it wants to "provide a more unified and consistent look and feel for Google Play," which it says will provide a "higher quality user experience." Not that it won't do anything for the app developers. Google says this consistent icon appearance will help it better showcase developers' games and apps.
Things that are NOT allowed: