I was kind of disappointed quite awhile back when I read that the wizard class in D&D Next would use the pseudo-Vancian system from previous D&D editions. Not enough to call it a wash, as I figured that it would be close enough to 3rd Edition that I could crib the optional rules out of Unearthed Arcana to make something closer to what I wanted. When the sorcerer and warlock were released in a playtest update, some considered having several spellcasting classes--each with their own spellcasting mechanic--to be a sort of olive branch to those who do not like pseudo-Vancian magic.
Whether you wanted that, or spell points, or encounter-based resources, you could just pick your class and be done with it. The problem with this approach is not just a matter of mechanics, but the class’s concept: there is more to wizards, warlocks, and sorcerers than how they manage magic. In other words, what if I want to play a spellcaster who learned magic by attending an academy, but would prefer spell points or spells that refresh without requiring a good night’s sleep?
Arcane traditions seem to be a way to address this. Rather that divvy up mechanics into separate classes, they can provide packages of mechanics and let you choose the one you want. I do not mind classes sharing mechanics, so long as the mechanics back up the flavor. Mearls states that they will provide world background and flavor for each system, and I am hoping that they take the time to make the explanations make sense in context of the game world (something that pseudo-Vancian magic has always failed to do).
Unfortunately arcane traditions will not make an appearance in the upcoming packet. On a related note, I wonder what this will mean for the sorcerer and warlock?