It's pretty much guaranteed to not be updated within the next year. A lens as significant as that isn't likely to sidestep the rumour mill such as a new 18-55 can, and from rumours to physical product on the shelves can take quite a few years - just look at the 100-400 mk II situation.
It was only released in 2010, and before the advent of the Canon 200-400 it was described as the best zoom lens in the world. No third party or rival OEM manufacturer has a genuine answer to this lens. There's clearly not too much to improve.
Go for it. It's a simply great addition to your 24-70 mk II