What’s wrong with an activity like writing a newspaper article about Pokemon GO? Doing such an activity will give pupils a chance to practise spelling and grammar; practise certain conventions and styles of writing; and practise structuring work.
All this is true. My objection is that, if the task were about a topic of cultural or literary significance, pupils could be doing all of the above and practising applying newfound, important knowledge.
Two for the price of one, as it were: we don’t lose any of the benefits of practising writing, but now we’ve got the added bonus of knowledge acquisition.