Will this ever happen?
No.
It has happened…you missed it.
No idea really (which is about the only answer you can really expect) but actually if you consider that much of the official reasoning for ending the upgrade path was high cost of unique packaging and storage/distribution against very few sales.
So just maybe when Sb start providing downloadable purchases, they will be more likely to consider it??
If you REALLY want Nuendo, your best bet is to keep an eye out for a used copy. You can fetch them used for $850-on up with the NEK. And, if you see someone selling it for over 1K, you will see it unsold for months because it isn’t all that popular and people will not pay that much for it. This comes from 1st hand experience as a buyer and eventually a seller.