You make two excellent points there.
I would LOVE to have more prominent targets. Up until the Emperor's murder, there were barely any notable targets, aside from Vittoria Vici. Even just more well-known characters, even lower than Jarls, would have been interesting (Personally, I wouldn't have minded getting a contract against Nazeem. Sure, I always kill him, but I'd love to be paid for my eager blood-spilling.

)
Next, I would love for it to last longer as well. In the Thieves Guild, you had many missions leading up to the final accost on Mercer. I think more assassinations (And no, I don't mean those so called "radiant" missions the Night Mother gives you. Those are so dumb) leading up to the Emperor's murder would have been fantastic.