I personally can’t taste the difference between beans that have been in the hopper for a day vs beans that have been airtight stored until the moment they hit the burrs (which is unlikely anyway given the journey a bean goes on from roast to your door).
If we are talking 3+ days in a hopper then perhaps it’s a different story.
I single dose for filter but not for freshness reasons, just so I can rotate a few coffees at a time. I find single dosing for espresso, especially making 2 or 3 coffees at a time is just easier grinding on-demand.
I suspect the popularity of the Niche being recommended as the home grinder for a long time now has also helped boost the popularity of single dosing.
On your timed grind point, I tried extensively to find a reliable timer grinder and due to the variables involved - mainly weight in the hopper, I haven’t found a timer that consistently produces satisfactory results. Grind by weight would be ideal but you pay a huge premium for that privilege.
I might be totally wrong but I think we are going to see a shift away from single-dosing in espresso.