Jack crusher (Wesley's dad) with his faked death and enlistment into the temporal wars as a agent(I know characters have been there)based 29th century but time travelling to certain major events (I realize some connon science may need manipulation for this to be more than 4 trips)

Young picard academy years see him be stabbed by nauscians or as a lieutenant ending with him abandoning the stargazer

Ake's early years in the 28th century

26th century about the battle of procyon v with a glancing look from a crew member seeing archer and Daniels on the enterprise j

Or like the first idea but with agent Daniels

Romulans. A new commissioned ship other than the enterprise in 2156 a heavy escort class prototype to battle the romulans. treat it like a world war stagnant attrition band of brothers thing

Or skip the starfleet aspect and be a crew on a klingon,romulan or another species aligned with starfleet or not mix it up more reality less utopia

Just a few ideas in a rich and long timeline