I'm surprised more hosts have not picked up on this thread.
:::Rant incoming:::
The most biggest gran-glorious most massive limitation of cPanel relates to not allowing the seamless breakout of different services to other servers- most glaringly the lack of integrated separate mysql server support, separate mail server support and of course NAS.
CloudLinux may have contributed some to the improving high availability by constraining individual account usage, but without the ability to use network storage more efficiently it can be a real bear to to scale up cPanel hosting- which is why the C word has taken on such intense discussion lately (in some measure due to cPanel failing to develop their "App" with an eye toward scalability IMHO).
It seems to me that cPanel's philosophy is, "just buy more hardware," when the world is going a totally different direction (aka, you may have heard of that "Cloud" thing...).
So many of us are scratching our heads going, "Ok, I can't leave cPanel because it's what I love, but I need the scalability of the Cloud and FEWER not more servers to service..."
Personally, I don't necessary need to lemming off the Cloud services cliff, but what I do need is the ability to downsize my server farm, utilizing just a few appropriately powerful servers set cluster-like, so that I can scale my business, not drown in the fear of amperage overloads and the decay of excess hardware.
Enough said?