To do that, the screensaver would need a reliable data feed. Is real-time futures data available for free that can also be openly distributed? I suspect that CME's policy on distributing futures data would prohibit such an application. I know CNBC and other cable channels broadcast live tickers, but I recall pledging not to rebroadcast market data when I signed up for market data through my broker. Probably better off just leaving your charting app running 24/7.
https://download.cnet.com/CoolTick-Stock-Ticker/3000-2057_4-10050065.html not a screensaver. You could just change the font size to the largest in your quote/charting program and save as a new layout.