This paper presents the prospects for periodic magnetic nanostructures in the form of magnonic crystals on polymer substrates. Indeed, arrays of magnetic nanostructures on flexible substrates are promising for microwave applications in the GHz frequency range. In particular, the mastery of the potentially coupled physical properties (magnetic and mechanical) allows one to consider devices for microelectronics in general, combining the microwave properties of spin waves with the lightness and conformability of polymer substrates. However, there are still scientific hurdles to be overcome, particularly with regard to the reliability of these systems, which is the focus of this review. Subsequently, we propose a general state of the art, a summary of the precursor works, and a general strategy for the optimization of these systems and their future possibilities.