First, I don't think GUI is essential unless your project mark scheme states that, but I still recommend you to achieve a GUI project as it can shows sufficient complexity on UI design. However, CLI is also acceptable, only if you can show that you make good use of your A Level knowledge, such as database, sorting and so on, and you have to explain why CLI is more suitable to your project. Just remember not to say that you can't design GUI so you choose CLI, you should say some reasons why CLI is better to your project.