I wonder how many souls an endgame person accumulates in a month.
My guild suggests 300 trophies, that would be 100 pvp fights. Lets double that, at 100 souls per win (assuming you're in full farm mode), is 20000 souls/wk or about 80000 / month.
I get about 1800 gold keys, 900 commons 300 rares, that is 4500 + 3000 = 7500 / wk = 30000 / month
500ish glory keys? Works out to about 6000/wk = 24000 / month
Not sure on gem keys, event keys, or using acrued gems/gold on them, but lets call it another 20000 souls? That is a total of around 155,000 souls a month disenchanting everything without doing any explore farming.
If Mythics cost 250,000 souls to craft you couldn't keep up without a LOT of extra effort, but it could let you target ones you want/need while trusting to the random draw for others. Which is why I don't think such an idea is bad.