GDPR abiding blockchain systems are feasible. Jurists, programmers, and other experts are increasingly working on this aim nowadays. Still, manifold blockchain networks functioning out there suggest a new generation of data protection issues brought about by this technology. Some of these issues will likely concern the right to erasure set up by Art. 17 of the EU data protection regulation ('GDPR'). These cases will soon be discussed before national authorities and courts, and will likely test the technical solutions explored in this paper, such as hashing-out methods, keys destruction, chameleon hash functions, and more. By taking into account matters of design and the complex architecture of blockchains, we shall distinguish between blockchains that have been thought about to expressly meet the requirements of the EU regulation, and blockchains that, for one reason or another, e.g. ante GDPR designed blockchains, trigger some sort of clash with the legal order, that is, (i) matters of principle on e.g. political decentralization; (ii) standards on security and data protection; (iii) a mix of them; and, (iv) social clash. It is still unclear how the interplay of legal regulation, technological constraints, social norms, and market interests, will end up in this context. Rulings and court orders will be instructive. It is a clash foretold, after all.