With Desynthesis on it's way with the next patch

[Yumi_umi]

IMO that was a weird reason! ^^; YoishiP has stated ARR was design as solo-enjoyable, so we should not have to concern for sociable.
As someone have said, the approach you suggested will make a lot of spam for WTS/WTB/LF trade ..etc

Moreover, it seems that good item might be desynthesize from untradable item, so maybe you cannot ask someone to desynthesize for you. ^^;

I'm pretty sure it'll work like the "request melds" feature. So that you won't be entirely giving them ownership to the rare items.
So it's a good idea for SE to go about it like this as desynth isn't the main attraction for crafting. It's sorta like frontlines as it is it's own kind of thing.
So boo hoo for all you crafters who want to do everything yourself lol
Just make friends and create a network of who's doing what and problemmmmmm solved.