I have a couple of ideas hopefully they are 50 000 words worth of ideas!!
One was inspired by some newspaper stories I came across on Trove. Trove is AWESOME!! Not only does it contain a database of items that are held in public libraries across Australia, but they have digitised newspapers, a database of photos and so much more!! I love it for the digitised newspapers and the wealth of family history information!
Anyhoo in a family that offshoots from my family tree by marriage is the Everingham Family. Matthew James Everingham was sentenced for transportation in 1784 and was transported to Australia in 1787 on the First Fleet. He died in 1817 when he accidentally drowned whilst on duty as a policeman. In the early 1920s there were articles appearing in the newspapers about the "missing Everingham millions" and rumours that Matthew had been from a well to do family and had been left a lot of money by his father. Only it was never claimed and subsequently was left to his descendents. The interest on that money meant that by the 1920s it would have been worth millions.
Anyway I found this story fascinating! It sounds like the plot of a novel already doesn't it? It's not my usual thing, but if I can't come up with anything else this is a good place to start.
The other idea is a bit complicated and I'm not sure how it would work out in practice, so I'm not going to share it here ... yet!