I guess one thing ROTJ lacks is the Deathstar killing Yavin IV scenario. There is a missing threat level to the battle, as there is no killer countdown.

WHAT IF

In the opening crawl, it is established that a collective of rebel groups have, in a decisive and surprise attack, captured Coruscant. (bonkers I know). The crawl could also suggest that the rebels have been going from strength to strength since ESB.

The Emperor however has escaped the rebels, and his location is unknown.

The Empire, now being under threat by the rebels, moves to take back Coruscant, and the rebel command move to defend it.

A twist later on in the story though, is that a second deathstar has been under construction, and the emperor plans to use it on coruscant itself.