For Brave to add and even update extensions to its browser will be painful and make the user experience with extensions bad. Please allow a easy way to import any chromium extensions into the browser. (So any Chrome extensions can be added)
Brave can add a disclaimer when your adding a extensions so users will know that not all extensions will work, some extensions could be invading users privacy by collecting data, and some extensions are not compatible with brave which could result into breaking the browser.
Another cool feature too would be to allow Firefox extensions to be installed and run but this would require a Firefox engine to be put into the browser.