The Allen institute (see e.g. https://twitter.com/danbumbarger?lang=de) and also Jeff Lichtman (https://lichtmanlab.fas.harvard.edu/) are very close to having solved the data acquisition problem (using very fast TEMs or multi-beam SEM) for cubic mm sized volumes, and we (http://www.neuro.mpg.de/denk) are also working hard on it. On the analysis side (i.e. automatic reconstruction), I am actually optimistic that it is mainly a software engineering problem (scalability to Petabyte-sized volumes, use tailored machine learning for remaining problems, e.g. to identify reconstructions that make no sense) and not so much a fundamental algorithmic limitation problem anymore. So 2 years from now, we should see the first cubic mm reconstructions.