As a certified legerdemain enjoyer I was pretty hyped when I heard there was a dedicated thief mythic coming.
Unfortunately, the pendulum swung in the opposite direction when I saw what it is.

For reference, this is the current state of the Shadow Queen's Cowl:

Light - Head
While crouched, you can see Witnesses and Guards through walls.
Successfully pickpocketing a Witness or Guard applies Distracted to them for 10 seconds, stunning them and decreasing their Stealth detection radius by 30 meters for the duration.

The problem with this mythic is that anyone with a decent stealth build is going to be virtually undetectable anyway, so the 10 second Distracted debuff is just useless.
My current build is also using the Ring of the Wild Hunt which means that not only would I be giving up all the bonuses of a Medium armor piece, but also 45% movement speed, for no apparent benefit besides highlighting Guards.

Instead, I would suggest changing the Shadow Queen's Cowl into the following:

Medium - Head
While crouched, you can see Guards through walls.
Patience is a virtue. Opportunistic pickpocket chance is increased to 100%.

What I mean by "opportunistic pickpocket" is that sometimes the prompt will turn green and rise by 10%.
This would instead rise to 100% for a guaranteed success, which I think is fair considering how slow it can be.

I changed it from Light to Medium for stat bonuses such as -7% cost of Sneak and -5% detection area. Light armor doesn't offer any benefits to a thief.
I removed Witnesses from being highlighted because I think it's a bit much and feels very cluttered.

Personally this is the only thing I would consider trading movement speed for because it would enable a slow and methodical playstyle which would be especially useful in certain areas with scarce NPC's that are difficult to pickpocket, such as Nobles.

What do you think?