Barrier to entry
At first glance, talents are pretty easy to use. They require a cheap reagent and moving buttons around or a macro. However, I still see lots of resistance to changing talents for every fight. The best part of talents is changing them around for unique circumstances, and there should be little to no barrier of entry to encourage that. The number of times that, at the suggestion of changing a talent for a particular fight, people have reacted in surprise, often with a “well, I just always run with Rushing Jade Wind”, is enough to convince me this is a problem.
The reagent cost should be removed because talents are a great feature. Many players interpret that cost as an indication that a feature should not be changed much, regardless of how cheap the reagent is. But talents should be changed all the time! Blizzard should encourage swapping as much as possible, both when leveling and when raiding.
How many times have you been leveling a character and wanted to try a new talent, only to discover you don’t have any of the reagent in your bags? If you want it badly enough, you can go to the nearest capital (because villages often don’t have reagent vendors), and buy a stack, but that’s a huge break in your game flow. Not being able to change in the middle of combat or a PvP encounter establishes all the “permanence” that you need to feel like it’s an important choice, while all that the reagent does is inflict a small but often confining barrier.
The reagent barrier is a vestigial reminder of the original version of talents, where they aligned closer to character customization in an traditional RPG sense. Back with the old system, you could say “I want my druid to be better at dodging, so she’ll take this talent” and you would rarely change that. (Though the more likely situation was: “I want my druid to be perceived as good so I’m going to use the same talent choices as everyone else”, but that’s a different issue.) However, talents are different now, and stats on gear will fill that character-customization niche already. You can be the brewmaster who wants to heal more and choose multistrike gear, and you don’t need talents to define your character’s uniqueness.
What we want to avoid is people saying “I want to be the brewmaster who specializes in burst AoE” and then talent into Xuen. That’s too niche, and makes such a specialized character feel bad when there’s no situation to match his choice in every encounter. Talents excel when they can be chosen to match each situation, and that choice feels better more regularly than when your niche character customization happens to line up with a certain encounter.
As a side note, gear and stats excel at character customization (at least for tanks) because every stat will at least be marginally useful in every encounter. The only exception is weird gimmicky fights (like the non-healing ones or no physical damage ones), but even then it’s unlikely you have 100% of your stats specialized into one place. You may be a crit brewmaster facing Lei Shi, but you probably have some haste and stamina, too. Stat specializations are not nearly so binary as talent specializations.
Macros
To further promote the idea that talents should be easily changeable, the necessity of macros and the tedium of dragging new talents to your bar is a barrier. More obviously, players shouldn’t be expected to find the right macro just to facilitate regular talent swapping. This is obvious, but the big limitation is that some tiers have a mix of passives and active abilities. I’d like to see a shared button for each talent tier. There’s a pretty big trade off here, but I think less is lost if a button is sometimes grayed out because you’re currently specced into the passive. It could be confusing, but at least it doesn’t discourage frequent use of one of the best features of the game.