It seems that, since the introduction of Nuage, Steinberg have decided to no longer publish their SDK in order to make it more difficult for other companies to develop products to interface with Nuendo/Cubase, presumably in the mistaken belief that this will force more people to buy Nuage. This action has contributed to SmartAv, the makers of the Tango control surfaces being forced out of business.
The Tango remains, in my view, the best control surface on the market, and rather than push me into the Nuage camp it has hardened my resolve never to buy any Steinberg hardware again.
It seems that Tango users are so attached to them that support for the controllers now seems likely to continue, although it may be slightly more difficult due to Steinberg refusing to publish the SDK information they have previously published for many years.
Well done Steinberg.