I thought something similar, too. In order to gain spells back, spellcasters just cannot rest and study/pray anywhere: they must be in very calm, stable places. Basically, they just cannot do it in a dungeon or out on the wilderness: they must return to an inn, or laboratory, or altar, anything like that. “Per day” spells then become “per travel spells”. This can be useful to limit the high number of spell slots in older editions.
Although, reading 2e, it implies this way, but apparently, the “per day” interpretation was more accepted.
Another option, perhaps together with the above, is the idea of “save points”: spells like Alarm, Rope Trick, Mordenkainen’s Magnificent Mansion, among others, just cannot be cast anywhere: we need special places for that; protection magic circles on the ground, which can receive those spells; or safe places like inns and such. Again, the idea is to create a “save point” system and control where players will rest.
Using them can get rid of the so-called 5-minute-work-day problem.
About Neo-Vancian…
I don’t know why some people call it that way. They are very different magic systems. 5e spellcasting is simply 3e Sorcerer with preparing (giving him even more flexibility); or, more directly speaking, 3e Spirit Shaman (Complete Divine). I call it the Charge system. I call the classic (pre-4e) Vancian as the Slot system.
The Sorcerer had a place in 3e: with the Wizard and the Cleric as slot system, and easier and simpler way is represented by the Sorcerer, as charge system. However, everyone being charge-based? Not my cup of tea.
