If you already have the serial code and you have already decided that the thesis framework is accelerating this specific code using OpenACC then the "hottest" topics could be "which adaptations of the original code/algorithm can be done to help OpenACC in improving the application's performance" and "how does your proposals work on different GPUs (if you have more than one available), i.e., how general they are".
Of course, a comparison with the corresponding CUDA implementation can also be interesting.