Since the coining of the term, altmetrics has evolved into a hot topic in science, science policy, and the wider public. There are, however, some discussions on how altmetrics will develop in the future. What are the challenges of designing, implementing, and using altmetrics which need to be addressed in the coming years? How can these new metrics provide benefit for different user groups? On the basis of an extensive landscaping effort, we have compelled a list of strengths, weaknesses, risks and opportunities for altmetrics.