Would that work?
It offloads all dongle work to iLok so Steinberg doesn’t have to worry about it.
Steinberg could sell an iLok license to those that want a dongle license, and those that don’t just buy regular Cubase license.
I think that is impossible. They need to re code all the old versions like VSL is doing. If it was easy VSL would be out by now with ilok versions which is just a plugin compared to a vastly complex Cubase and Nuendo.
What might be possible is to generate and send non upgradeable, nfr back up licenses to people that want to stay up to version 11.
So before the servers shut down they can activate a spare e licencer and keep it safe as a back up.
Two reps have said on other threads that moving from any kind of hardware dongle is very deliberate in their decision. I can’t see them developing their own system and then moving to a third party UNLESS it goes very bad. 
I haven’t a clue how well ilok products are protected, just had a google search and it seems that hackers have got around certain iterations of it, perhaps that cloud/dongle flexibility is also an Achilles heel?
I’ve not used iLok dongle in years, everything I need is on their cloud system.
It wouldn’t make sense for us to develop our own licensing system, and then pay PACE to use iLok. There’s zero chance of this happening (or as close to zero chance as it is possible to have, given that we cannot reliably predict the future).