clearstream
(He, Him)
Experienced players use T1-2 (entire) as much or more than new players. Cutting things they would value could well lead to dissatisfaction among an important cohort.I like the concept, but I would move the bar. The first book needs material on how to play the game, what skills are, how to do combat and a bunch of stuff that the higher level book does not need. The lower level book also needs to be as low a barrier-to-entry for new players as possible. So I'd have the low level book be 1st to 8th. 4th level spells are pretty cool and are half the spell lists, there's a good runway to plan ahead, but it is leaving out a lot of things that aren't needed for new players.
I feel designers should create what best serves players (which will then sell books) rather than building for overt monetization.8th was picked so (a) it doesn't end as soon as you get 4th level spels and the like, and so that they can include "8th level+ feats" so people can dream and drool over what their character will get at later levels.
Another thing WotC might appreciate is that since their surveys say most games go to 10-11, there's build in incentive to buy the next book for players, as opposed to just sticking with one.
I'd speculate that a really high value T1-2 PHB will sell more T3-4 PHBs than nickel-and-diming players would.
PHB 1-10
APHB 11-20