Huh. New trick to this old dog.
I guess I/we have always just assumed - perhaps incorrectly - that by-the-book spell studying happens all at once at the start of the day and that's it. But I suppose it doesn't have to.
Maybe the grey matter is mis-remembering, but IIRC, Rob always allowed one to "shuffle" spell points from one memorized spell to another. I know I allowed that.
Question: the way you read/run it, does the Archmage (or any mage) have to rememorize everything from scratch each time or just refill what was cast the day before?
I have it as a "re-memorize whatcha done used the day before."
IIRC, you still use the "no need to memorize lower-level spells" rules in the spell-point system, yes?
What the game doesn't have - and IMO it's a huge oversight - is mechanics that allow people in the setting to (slowly) gain levels without adventuring: the stay-at-homes who become the high-level NPCs that dot these settings.
If the stay-at-homes do things that are (new) and would give Xp, why not? I had to think about this because I've got a city setting where there's a slum of about 500+ people, struggling to make ends meet. I have established that an NPC nature cleric has set down roots, and is blowing her Spell Points every day on vast quantities of Goodberry, just to feed folks.
The PC nature cleric is now contributing on a regular basis. I gave that XP, but I'm giving it diminishing returns.... although there may be in-game rewards later, most likely as the poor who are aided will remember the PC cleric and be more likely to help/give info or - at a later stage - be recruited.
The problem is that it is anti-social mechanics. It's not necessarily fun for the group, nor is it necessarily fun for the DM, as it sort of forces you to create stories that don't have a lot of time pressure. And taking time pressure out of a story kills the fun.
Bingo. By shortening memorization times, the mages now can do other things.
I run on a spell point system rather than a spell slot system. This gives some flexibility. Mages need only memorize spells that are (a) new to them OR spells that are the highest level they can cast. The time required is 2xSP. Thus, memorizing a fifth-level spell (which requires eight spell points) is a 16-minute effort.
The acquiring a spell per level is its own rule (DMG page 39) separate from the training rules (DMG page 86) which includes both training under a higher level character and self training.
I've played and DMed under that model, and I don't like it in either form. The mage-training-from-another was part of a larger mechanic in OD&D which, IMO, was actually a "let's claw back some of the gold we've given you" process. I do not require most classes to be 'trained' as it were. People just 'become' better, with sufficient XP, a realization that comes after a long rest (usually after a night's sleep.) The exception would be certain levels of cleric, specifically seventh for nature clerics, and maybe more because I haven't got there in a totally revised system.
This is one of the (few?) things that 5e got right with spellcasters. I bump to fifth level, and I automagically get "known" spells. I don't need a teacher, I don't need to find a higher-level being... I just know stuff. I like that, esp. since I want to have mages be freaking rare as all get out. The problem I had with the old way is that now I needed to have mages around every time a mage PC bumped, and it's hard to have a "mages are rare" them when your PC can track one down when needed.
None of that makes the slightest bit of sense in the context of the rules.
1) You can't even make martial magical items until you are a 16th level M-U, so in a low magic setting there should be no magic swords (for example). The production rates for such items is lower than the rate they'd be destroyed to crushing blow, etc.
I shifted game balance by giving clerics the power to make magic items - or at least lower level/mundane ones. "Create Potion" is a third level spell for some clerics, and generally involves preserving the properties of a herb....