"I haven't thought whether it would be an issue if it works in one direction only (halvings, but no doublings), but it might."
Yes, I'm not brave enough to propose "doublings" yet... ;) frankly speaking - I'm unconfortable enough with undermining Holy Graal 21M I wouldn't do that without my sureness that something must be done sooner or later with this long-term embedded problem. Yes, there is no such thing as a free lunch - I'm a fan of Milton Friedman.
"It's not hard to imagine that even Satoshi may not have gotten it 100% right."
Very true. Satoshi forgot to implement free market between active and passive users, unfortunately.
When you realise that he started the system from one edge case - i.e. inflation starting from infinite in first block in fact, and stakeholders were able to survive this "early" phase with enormous annual inflation only because of "Numbers go up" (i.e. due to system expansion) - and system is simply going by design to the second edge case, i.e. with zero annual inflation.
I don't know if we could find any example of staying in the edge case - as a healthy state for any system. And we are trying to grass-root building of alternative financial system - maybe the biggest challenge I met in my life...