Tragic when someone dies on the road, but I don't think the 'ghost bike' would help.
We already have way, way more roadside shrines and flowers than I am entirely comfortable with. I used to pass three such shrines on my ride to work in the Herefordshire/Gloucestershire borders. The best they ever look is slightly scruffy and at worst they look unkempt and forgotten. I realise some might find that view unpleasant.
It used to be a south European thing to put up roadside shrines or makeshift memorials for people killed in traffic incidents. I recall seeing them bunched together at key Alpine bends and near the tops of Balkan mountains... That can be poignant. Seeing their bland UK counterparts at the exit of a Shell petrol station is less visually arresting.
Now I see these well-meant but unattractive markers all over the UK. I've heard them referred to as roadbling... which is tasteless but is how many people see it.
As a possible alternative to the 'ghost bike', I first saw in southern France about 15 years ago rows of lifesize, black-painted cut-out figures beside the road at locations where there had been deaths.
They were erected by the local authorities and just before or after the (for example) seven cut-out figures, there would be a sign saying "7 people killed here in traffic accidents in the past 24 months" or similar.
I recall one or two such displays having child-sized cut-outs for younger victims... which really does chill. From a distance they just looked like seven people standing by the roadside.
That system seemed to have a profound effect on people. I'm not sure a 'ghost bike' would do much, particularly if people didn't know why it was there.
It's a clever idea, but it may end up just looking like a bike someone forgot to collect.