Bingowings said:

Beyond the obvious difficulty of creating new footage for the Imperial Capital sequences the main problem is the lack of an immediate threat or boon to push the Rebels to make such a bold move, especially after getting such a kicking as seen in ESB.

Re-taking the Capital would be the capstone of the Alliance's struggle (Episode IX material).

The only thing that would motivate them to make such a move so soon would be something that could threaten them with total and instant disaster or some piece of intelligence which would make the plan seem a viable option.

Something like a Death Star, or maybe two or some sudden and soon to be fixed weakness in the Capital's defenses.

Without a danger of that...magnitude (ahem) or an opportunity of that scale what's the rush?

I'm not dismissing the idea out of hand but posing it as a question which might open the door to thinking about solutions.

You're right. There would have to be many reasons for such a dramatic attack.

A second Death Star could remain one of the major motivations of the attack, but not the focus of the scene. The Emperor would still command it to assault the Rebel fleet in a show of power, before the Super Star Destroyer is unexpectedly sent veering off course, crashes into the incomplete structure of the Death Star and destroys it.

Their opportunity to attack the Imperial Palace would be a secondary motivation. In attacking the Death Star orbiting the Imperial Capital they are taking a risk they would not normally take, and they wish to maximise the potential military value of this attack by also attempting an assassination on the Imperial government. Even if success is (as always seems the case for the out-gunned rebels) a distant possibility, they have to make the best use they can of this brief moment in which "the Imperial forces are spread thin throughout the galaxy in a vain attempt to engage [them]".