A QOL change entirely because I'm lazy

[Verlyn]

Yes, this would be a very convenient change.
For that matter, crafting from retainer inventory. Please make it happen.

There is one thing to consider about this...

When you sell items, you sell to a specific NPC... if you add a sell option on the retainer... to which NPC is it selling to?
You must not forget that everything in the game is done with the role-play aspect of it in mind.

You are way over-thinking this.