Hey Hist Ext buddy!! Surprised you haven't gotten a topic yet, my proposal was due last week
My teacher tells me to do a topic that has a great deal of controversy and debate behind it, enough to sustain an argument and better if you can include a judgment (evaluate)
What periods of history or cultures are you interested in? Eg French, English, Japanese, Chinese, Australian or the Revolutions? Remember that this is History Extension, which means you aren't supposed to write history but rather historiography, yeah sure you can write about some background information or context but that is not the point of the project. Essentially don't make your project too History-like, it’s hist ext so u gotta make it historiography related, just talk about the reasons why historians wrote that particular way.
Also try to avoid cliches, can't remember any specific ones but make sure to ask your teacher if your topic seems too overused or not. Mine is on the French Revolution and it's about the historiography of the French Revolution 'To what extent does Marie Antoinette showcase evidence of causation of the French Revolution in the 18th century? ' another student in my school did ' Does Alexander the Great deserve his title?'
But yeah maybe just base your project interest/topic from your Preliminary investigation?