Been discussed before. I wouldn’t want to propel the game any farther into the future, as a 5th age would infer.
I’d rather a late game tech or Renaissance be researchable that allows you to build visual customizations for your empire. Make embellishments on your stuff that is mostly or entirely for looks. Plant flags. Make roads or cobblestone paths. Put gilding on structures. Find marble quarries perhaps to mine and make marble sculputres. Make cemeteries. Make arches.
Sometimes I don’t like the game to end. If I’m dominating the map and just want to keep growing econ and spending resources, building more walls and castles, at this time I wish I could stay making my empire more cool to look at. Racking up 100K in resources is nice, but just wish could spend it on some cool new stuff. Using it on the typical old stuff of castles, walls, and wonders that you’ve been able to do all game and for 20 years is not as invigorating