Regarding the "desynth all" or "quick desynth" idea, community reps responded on this issue before, actually.

Quote Originally Posted by Grekumah View Post
Greetings,

At this time there are no plans to introduce any type of “Quick Desynthesis” feature that would automatically desynthesize items in repetition. The amount of time to desynth an item is quite short, so we'd like players to do these one at a time.