This is an interesting idea - there are always 'brick walls' in genealogy. I thought I'd list four in no particular order. If there is an afterlife, I'd want to spend the whole time interviewing my ancestors and clarifying these mysteries. There are mysteries that are, practically speaking, insoluble. Questions like: "tell me about my ancestors in Ireland" have the answer: "dear matt, we smoked those Irish records up for fun, from England". So there's no point putting down a 'things I could discover in a parallel universe list'. Those are the people I'd grill in heaven - I'd turn their cloud into an interview room, turn the sun on their eyes like one of those lamps, and grill them over their farming practices and why they waited three years to baptise my ancestor.
But to set down genuine solvable questions - things I would like to answer with a little application and luck - is worth doing:
1. Where did William Smith come from? Wow this is a tricky one. WILLIAM SMITH (http://thehistoryofmatt.blogspot.com/2009/12/william-smith-abt.html). He was born abt 1836, married Helen ROBERTS in 1869 in Sydney (herself somewhat tricky) and they lived on Lower Campbell Street, Sydney. He vexes me so much that it is their street on my 'History of Matt' banner (under OF). The birth certificate of two children reveals he was a Van Driver or Carter, born in 'Hamburgh, Germany'. He died in 1874 at Liverpool - presumably on the road for work - leaving three children. But was he really German (Wilhelm Schmidt) or the son of a British soldier? How did he get to Australia? Maybe a clue lies in the fact that his second son was 'Alfred Elpinstone Smith' (born 1873). A William Smith arrived in Australia on the Elphinstone in 1840 - a clue to descendants about his arrival? This William was aged 5 (so perfect age), the family was Baptist, and of 'Aughall' (father, George, 36, a labourer).
2. What happened to Harriet CASTLE nee LEWIS? (http://thehistoryofmatt.blogspot.com/2008/07/search-for-death-of-harriet-castle.html). She came to Australia with her husband Isaac, and they had children in the Bathurst district till 1872. Isaac died in 1911 and his obituary states she predeceased him by a significant period. He is also not buried with her at Cowra. They registered the birth and death of every child - so I think her death was incorrectly indexed by NSW BDM.
3. Moloney and the Earl of Emly. This would take years in the Irish archives. My ancestor John Moloney came to Australia in 1864, and was a teacher. For whatever reason he came, family memoirs all state that John MOLONEY was a cousin on the Earl of Emly. Many of the landed gentry in Ireland sponsored townsfolk who emigrated to Australia and it may just be a simple connection such as this that is garbled. But with Irish birth records the way they are, to solve this requires a letter surviving.
4. Who was Henry PRIESTLY's father? Henry was born abt 1838, but his mother Catherine SLATER married Samuel PRIESTLY in Sydney in 1840. Catherine arrive in Van Dieman's Lane in 1837 but I haven't been able to find a baptism in either VDL or NSW for a Henry about this time. Was Samuel his real father, and if not who was it? Perhaps Catherine fled from VDL to Sydney when she became pregnant. Did Henry even know his Samuel might not have been his father? In 1858 when he married, Henry stated his father as Samuel (http://thehistoryofmatt.blogspot.com/2008/06/samuel-priestly-and-catherine-slater.html).