I think Itachi is the most plausible suspect, but I'm going to entertain a possible alternative for the sake of thoroughness.
Rock benefits.
In order for Rock to pull it off, they'd need two things: Akane's blood and the ability to infiltrate the Sarutobi compound and leave no scent.
Instead of a tower mole, what if Rock sourced the blood from Akane's body? We already suspect Rock was responsible for Akane's murder due to the proximity to the border.
An interesting theory. As you say, it's nice to have an alternative even if it's not that likely.
It's true that Rock benefits from anything that weakens Leaf. We were also told that they have a motive for killing Akane: revenge for her capturing the Tsuchikage's husband. Moreover, they don't need to exactly predict whether the plot is going to kill Asuma / Kakuzu / Hidan. Anything to brings tensions between Leaf and Akatsuki is good for them. Asuma dying, and/or an Akatsuki member dying and bringing retaliation on Leaf, are great but not necessary for the operation to be useful.
We don't know much about Rock's infiltration ability so let's assume they have the capability for now.
Yeah that's one of the reasons the odds that it's Rock are rather low.
The problem is would Rock have had the right intel to know that framing Asuma would get him killed by Hidan?
Rock would need to know that Hidan was tracking Akane. Was it widely known that we'd set Hidan on the trail?
Placing a bloody shirt in Asuma's room wouldn't work to frame him unless the perpetrator specifically knew that Hidan was tracking Akane's traces via blood.
If they killed Akane, maybe they were paying particular attention to anything related to her death? But that doesn't explain how they got access to the intel in the first place. Hidan's visit to Leaf was very public, but I don't know how widely known his mission was, that's a good question. It might have been highly classified since anything that brought attention to Akane was bad. On the other hand, Hazo is known for interacting with Hidan; him asking Hidan to track her murderers for the sake of revenge, without particularly trying to hide it, is another way to hide the fact that Asuma is also very interested in the investigation. I think that's what they were trying to project when giving the mission to Hidan: Asuma reluctantly allowing Hazo's whims. If you're not sure you can rely on Hidan to keep OPSEC anyway, you might as well prioritize setting up the right narrative. You also need Akatsuki themselves to buy this line.
Actually, I think the hardest thing to explain intel-wise is still how they knew about Akane's mission. Ino interrogated all the Tower's ninja staff, Shikamaru interrogated the Tower's civilian staff, Ino went through their immediate family and friends...
Maybe they planted it because they hoped Hazou or the Inuzuka would find it? Cause distrust between Hokage and clans.
Strictly speaking all they'd need to know was that the matter was being thoroughly investigated, and that Leaf had some way to identify the blood - which wouldn't be hard to guess if they knew Hazo was the Dog Summoner, Akane's clan head, and cares about his own people enough to pick fights with a kage, none of which are particularly secret.
I don't buy this, because multiple characters have stated that the evidence doesn't make any sense, and that only Hidan would ever think it points toward Asuma being guilty. Even if it's Rock, I still think it's more probable that they knew about Hidan's investigation and had enough intel on Hidan to expect him to react strongly, so they put the shirt there for him to find.
To sum up, the main arguments in favor of Rock being the culprit are that they have clear motives for both killing Akane and framing Asuma, and they don't need to accurately predict how things will unfold: all outcomes are good for them. Arguments against are that we don't know how they infiltrated the Sarutobi compound without even Canvass picking up anything (very hard), how they know about Akane's mission so that they could kill her (very hard), how they knew about Hidan's investigation (maybe easy if Asuma and Hazo went for the "hide the true motivation, not the mission itself" strategy), and how they knew that Hidan was likely to have a strong reaction (medium? Hidan doesn't make any efforts to hide his personality, but that's still a bit specific).
