So for the purpose of planning, I have to assume "no ETA" for single server updates means never. So we're left with
a) Use old version for two more years
b) Switch to flexible server, which is in preview, but not really.
Switching databases in production is inconvenient, to say the least. When setting up the single server, I assumed the version policy would be honored. If you have to frustrate your users please do so transparently and communicate that you want us to switch to flexible server and that single server won't receive updates.
I saw that version 14 for Hyperscale was released within one day. That' impressive and tells me the team cares. But when I have been waiting for version 12 for two years, it lets me know that the priorities lie elsewhere and I need to migrate.
Don't take my rant as a vote for a single server update - just letting you know that I lost faith in the product.