You’re right about the increased voltage for certain signalling functions, but it goes deeper than that.
If you’ve only got 1.2v on tap you can use some pretty clever fast voltage splitting techniques to make it about 2.4v functional.
Now you wouldn’t think it would make a huge difference, but getting this to over 2v makes a huge difference to the design of the spacing and mass of the components within the condenser mics. Consequently you can make mics with lower noise floors. Which in turn yields to wider input ranges and more natural sounding hearing aids.
And as we ‘all’ know as you increase the voltage, you proportionately drop the current; so lower battery drain. So if you design hearing aids to take advantage of this, making a 312 version is going to become harder. The voltage produced by a standard 312 cell has been one of the biggest design constraints of modern hearing aids.
So aside from arguments about convenience, the driving factor for new innovation is likely to be the extra voltage on tap and what the engineers are able to do with it.