The wide availability of mobile devices like smartphones and tablets among students as well as the included positioning technologies, high definition cameras and other sensors, together with continuous Internet access bring many new opportunities for developing mobile applications supporting learning activities. However, there is an immense fragmentation of operating systems for mobile devices. HTML5 is a promising approach to tackle this challenge. Mobile web applications run within browsers and nowadays, most mobile devices possess a browser that interprets HTML5. Nevertheless, the educational domain seems to ignore this potential and relies on the development of native applications. In this paper, we analyze the opportunities, advantages and drawbacks of developing mobile applications supporting learning activities with HTML5 compared with developing them natively. To illustrate our ideas, we present a couple of showcases that already rely on HTML5, which allow us to further review the development opportunities for mobile HTML5 applications in general, as well as specifically in educational settings.