Okay, you've added a requirement. Poll the current cursor position after the first hit-test sets the dragging state and call a function to render your object with X% opacity at a higher Z level than anything else. Your 30 minute job has become a 60 minute job.
> As is deciding whether the ghost should affirmatively snap out of and into the source and target containers (that is, whether the destination container should appear to “make room” for the ghost at some point), whether there’s a transition on that,
Most applications don't go this far, including your operating system like Windows that sets baseline UX expectations, so you're well beyond the default expectation for drag-and-drop. If someone asks you to implement drag-and-drop without specifying they want all the bells and whistles, and you respond it's going to take you a week because you're planning to go all-out beyond necessary business requirements, they'd have a valid reason to be like "WTF mate?". Also this is still pretty paltry and not a week's worth of work.
Do you remember what browser testing was like?
Remember the quirks of browsers’ different understanding of transparency, of z-index, of events, of DOM compliance?
I think the suggestion that getting it right could take a week in the context of a particular application is actually not particularly hyperbolic.
Mind you, I was doing cross-browser testing long enough ago that I am one of those people who can say they independently invented AJAX in-house.