There has been success in growing birds in plastic see-through artificial 'egg shells', basically cups that hold the yoke. They use antibiotics and other measures as well as temperature and moisture controls. With that solved in practice, locating the nucleus is probably just a matter of technique and methodology. Dye based (fluorescence) is one possibility. High contrast imaging, point tracking, automated microscopy, and and an agitator to move the yoke around in the search process (without damaging it or physically handling it) would likely solve the problem of locating the nucleus. These are trivial ideas. Article is probably just a disguised advertisement for the tech the piece discusses. Thats why they're not going with the more straightforward options. Also I see of no reason why microfluidics couldn't be used to establish a testbed platform for producing spermcells for various species as a sort of "artificial gonads".