Ext plugins let you use internal APIs and even let you overwrite Liferay DXP core files. This puts your deployment at risk of being incompatible with security, performance, or feature updates released by Liferay. When upgrading to a new version of Liferay DXP, you must review all changes and manually modify your Ext projects to merge your changes with Liferay DXP’s.
During your upgrade to Liferay DXP 7.2, it’s highly recommended to leverage an extension point to customize Liferay DXP instead of using you existing Ext plugin, if possible. Liferay DXP 7.2 provides many extension points that let you customize almost every detail of Liferay DXP. If there’s a way to customize what you want with an extension point, do it that way instead. See Finding Extension Points for more details.
For more information on Ext projects, how to decide if you need one, and how to manage them, see the Customization with Ext section.