Answering my own question - blimey, it IS possible! See answer here on the Steinberg forums:noiseboyuk wrote:I wonder in fact does it mean you can only get one grace period in the life of any one license? And as a bonus thought... if 10 came out and it was poo, is it possible to hold on for another full year?! The text actually suggests this might be possible...
https://www.steinberg.net/forums/viewto ... 2&p=725146
So you can buy an upgrade now, do NOTHING WITH IT, then just wait til Steinberg releases a version worth upgrading to. If you played a long game and were really patient here, you could save many hundreds. More realistically, it does take a lot of the risk out of this plan - if 10 turns out to be terrible, just hold tight for 10.5.