I've worked quite a bit on this object. The Perseus cluster is one of the most interesting galaxy clusters in the sky and is the X-ray brightest (and so well studied). There's star formation, bubbles of relativistic plasma bubbles generated by the central black hole, presumably heating the surrounding gas and preventing catastrophic cooling, sound waves generated by the inflation of the bubbles, a giant nebula producing emission lines. You could give several talks about this object... Some nice pics here of the central galaxy, NGC1275: http://www-xray.ast.cam.ac.uk/papers/ngc1275/
We'll have to wait to see if this result can be replicated by others and we'll look at the results from ASTRO-H when it launches. If you examine at the original paper (http://arxiv.org/abs/1402.2301), it's certainly not cut and dried dark matter emission (yet).
It may be worth noting the significance of ASTRO-H to this kind of science (full disclaimer: it's a long time since I did any astrophysics so I am liable to get things wrong). The attraction of ASTRO-H is not just newer == better. In fact in several ways it's worse than existing X-ray satellites, for example it won't have the angular resolution of Chandra (so no pretty pictures) or the sensitivity of XMM-Newton (so bad for looking at very faint objects). Where it is designed to excel, however, is in spectral resolution, where it is about an order of magnitude better than the other observatories. This means it's going to be great at measuring the precise energy of incoming X-rays, which is essential for studying emission lines like this. If your spectral resolution is too low you'll find it difficult to detect weak lines at all because they get averaged over such a big energy range that they end up just looking like the background emission from the hot plasma in the cluster.
Once you have established that there is a line in the emission, good spectral resolution is also critical to determining which models are compatible with it. There's almost certainly a lot of ideas people can dream up that will fit "a vauge bump around 3.55keV", many of which will be eliminated once you have a better idea of the shape of the line. This is the sort of science that ASTRO-H should be good at.
Hopefully someone will correct me if I made any egregious errors.
Absolutely right - ASTRO-H brings new capabilities - high spectral resolution in X-rays which we don't have now. It's pretty exciting.
Beyond that, here in Europe, the European Space Agency has now approved our proposal for Athena (http://www.mpe.mpg.de/Athena), which should provide a large collecting area, high spectral resolution and pretty good spatial resolution. It's going to be a large technical challenge, which unfortunately means we'll have to wait until 2028 for launch. It requires development of a new mirror technology (based on stacks of silicon chip wafers!), development of a cryogenic X-IFU (X-ray integral field unit), which is going to provide spatially-resolve high spectral resolution X-ray spectroscopy. There's also a wide field imager, capable of mapping large areas of the sky quickly.
We'll have to wait to see if this result can be replicated by others and we'll look at the results from ASTRO-H when it launches. If you examine at the original paper (http://arxiv.org/abs/1402.2301), it's certainly not cut and dried dark matter emission (yet).