I can see that this idea is bringing in its fair share of discontent, but don't let's forget that Waldoff posed the figure of each of these new codices requiring 1.6 times the exp of a single Codex of Power. Let's look at the numbers:
Current Codex of Power System
Each of the five CoP requires 110 AAs.
5 codices x 110 AAs of exp = 550 AAs total to complete all five
Proposed Three-Codex System
Each of the three codices requires 160% of the exp currently required to fill a single CoP.
3 codices x (1.6 x 110 AAs) = 528 AAs total to complete all three
This is a net reduction in the exp wall for all classes, even those that "need" to do all three of the new codices.
Furthermore, the three-codex system would allow a class like Beastlord, for instance, to prioritize his options in order to receive the most important bonus first (such as Codex of Battle: 20% Melee, Pet Melee and Ranged Damage). This flat 20% bonus for melee and pet damage, which used to be achievable only after finishing a whopping 550 AAs worth of CoP exp, could be earned by the Beastlord after plowing through the fractional amount of 176 AAs. Should he wish it, he could then go on to pursue the Codex of Healing next, and after another 176 AAs (352 AAs total), he would have earned a 20% bonus to all his healing output, a bonus that, again, would only have been achievable after having plowed through 550 AAs worth of Codex of Power exp.
As long as the three new codices are coded to give partial bonuses while the player is working through them in order to stave off boredom and encourage their completion, I see this as a positive change.