I don't know about the open backed NDH30, but I can certainly say that the closed NDH20 is a fundamentally different sound from the HD490 Pro. We're not talking about lemons to limes here, it is apples to oranges, they're not interchangeable.
The soundstage of the 490 is not that much larger than the Neumanns, but it is a distinctly different experience, a step up in terms of tangible, "reach out and touch instruments" holographic imaging, with excellent positional accuracy. The soundstage itself is more analytical, not in the sense that it's less pleasant to experience, but that it better allows you to pick apart different sounds in the soundfield, and appreciate each individually.
The 490 Pro has a more separated sound, which changes the soundstaging and also increases detail retrieval, without ever really sounding analytical per se (at least with the Producer Pads). The 490 Pro is slightly brighter, but not colder, not any more sterile or dry. The 490 is noticeably less bright than a Grado, or a Kennerton Vali, the brightness and upper mids are not overcooked like in those obnoxious tunings.
The bass on the 490 is more analytical than the NDH20: you get more texture and detail, but a little bit less extension and low bass, giving less of a solid impact, despite giving an equal feeling of dynamic slam. I've tested it with techno and rap, it's simply different. The slam is still there, and the quantity will be there if you use a bassy amp (I'm using the Xbass on my iFi amp). Some people would probably say the 490's bass is spongy in comparison to the Neumanns, but I have to say, it's quite a detailed and articulate sponge!
Ultimately one has to acknowledge that both of these headphones are magical from a practical perspective, the NDH20 because it's a maximum passive isolation closed back and still sounds that good, and the HD490 Pro because it's 260 grams with light clamp force and still sounds that good.
I think the Neumanns will get to keep their outrageous cable, but... the HD490 might get an even more outrageous one, since its mini XLR connector can accommodate thicker cables. I do believe the ceiling for raw detail retrieval is probably higher on the 490, and I plan to hit it.