I don't know if anyone else has done this, but I ran at least 100 grade 11 lockbox missions to see just how lucrative (or costly) it might be.
I started out with 1 million credits even and I used a full-influenced companion for maximum time and result efficiency. At 4250 credits per mission I spent 425,000 credits. I ended up with 1,346,915 credits for a 346,915 credit profit.
I had 34 critical successes, 6 failures, and 60 standard successful missions. The failures still produced various grades of scrap. Each lockbox provided a random amount of credits, usually less than the original mission price but usually within 500 credits.
The critical successes gave 3 lockboxes along with a grade 11 mission discovery, two of which were slicing. The slicing mission discoveries did not reward any lockboxes, only sliced parts and for critical success more missions and legendary embers.
I ended up with 1081 premium scrap, 779 prototype scrap, and 226 artifact scrap.
This is clearly a lucrative mission, tempered by the length of time for each mission and that it can only be done one at a time.