Kind of good, kind of bad. For example, my pally is Prot/Holy and I tend to quest as Prot and run dungeons as holy; this means to build a holy set I have to quest holy? No thanks. Maybe buying the gear will fill this gap. What I used to do is choose a quest reward based on what I needed most. I may have pulled out healing bracers from a dungeon run, so I'd tank the tank ones from a quest.
Seem a bit limiting what they're proposing.