I could see the same thing doing well outside the US embassy in London.
Offer a US-visa sized passport-photo service, a locker to put your phone when you can't take it into the embassy and some tissues to wipe away your tears of joy/despair and you'd be in business.
Add to that a £10 glossy file to give the assorted papers of your $2,000 application that final touch of gloss and you could make a wonderful income.