Most of my Steinberg software was acquired when I was entitled to EDU pricing. All but one licence has subsequently been upgraded, becoming a retail licence in the process. The upgrade to retail status removes the restrictions on EDU licences: they cannot be used for commercial work and are Not For Resale. Steinberg only offers EDU discount on full licences, never on upgrades to a larger product or version updates, and does not include EDU licences in their periodic sales.
One possible strategy would be to buy Cubase Pro EDU now, then crossgrade to Nuendo when the next version of Nuendo is released. If Steinberg sticks with their current policy that you get the current version of a product on the day you activate a licence (not the day you purchased the licence), the crossgrade will not only switch you to Nuendo but update you to the latest version as well.
This means you likely can buy a Cubase Pro to Nuendo crossgrade when it is on offer (i.e. now!), then wait to activate it until a new version of Nuendo has released. Cubase Pro 11 EDU in the UK is £291 (plus the cost of a USB eLicenser if you don’t have one). The Cubase Pro to Nuendo crossgrade is on sale at £205. The full version of Nuendo is on sale at £504 (plus the cost of a USB eLicenser if you don’t have one). The current sale means there is almost no saving buying Cubase Pro EDU and crossgrading to Nuendo immediately. However, you could buy and use Cubase Pro now under the educational restrictions, then wait to activate the crossgrade until the next version of Nuendo is released, saving yourself a Nuendo version upgrade charge. If you have to do commercial work before the next version of Nuendo releases, you have the crossgrade code ready to activate, though you lose the ‘free’ version upgrade if you activate Nuendo 11 before the grace period for the new version starts.
There is an EDU version of Nuendo, but I would only buy this if you cannot purchase before the end of the current sale (when the crossgrade price will go up again) or are sure you will need the Nuendo only features before the next version of Nuendo is launched, likely in around six months. If Nuendo 11 is anything to go by, Nuendo is now on once a year releases with Nuendo launching a few weeks after the corresponding version of Cubase.
As @steve rightly points out, the official policies are those that are on the Steinberg website; no customer can guarantee that Steinberg will stick with their previous policies.