Most of the strategies on QC are daily based, would be good to see something faster, intraday and HFT, if possible.
I was thinking about these strategies ...
1. Leader - Follower, find two dependent assets, the first one initiates the trend, the second one repeats this action with delay, on Forex it usually happens between EURUSD and GBPUSD. On the Stock Market, I presume some main stock, like Amazon, moves and some ETF or index fund, like QQQ, goes after, https://alphaarchitect.com/2013/09/10/follow-the-leader-in-the-stock-market-it-works/
2. Closing gaps or continuation of a breakout on pre-market, e.g. if usually price of some stock is going up, but at some day on pre-market if falls down or goes up about 5%, then traders are tend to catch the spike and revert the price to compensate at least 2.5% of this move,
https://www.warriortrading.com/gap-go/3. Anything volume-based, if leve II and Order Book is not available, then would be good to see analysis of the market orders volume, e.g. find average volume for all stocks, detect volume spike, on the next day, detect where price keeps moving, catch the trend, I think this is how it should work, but there is no common opinion on how to analyse a turnover volume,
https://www.tradingview.com/script/mlzPTieC-Volume-Trend-Following-V0-1/