I like your suggestion. Didn't really think about having one or the other with a prime. Now the question with having one or the other with a prime is whats the perfect prime to complement either one. I think the 70-200 with a 40 would be nice but then how would you get those wide shots when needed?
That goes both ways. However, the 24-70 II and the 70-200 II are approximately the same price. A tele prime in the 135-200mm range is several hundred dollars. If you get the 200/2.8, you'll likely not use it after getting the 70-200 II. A 40/2.8 is $150, and given it's conveniently small size, it's useful even after having the 24-70 II.
As for wide shots, someone here (apologies for forgetting who) has pointed out that the 40/2.8 has an exit pupil that's basically at the body, so doing a quick handheld pano shot and stitching the resuting images together is quite easy with that lens, when 40mm isn't wide enough.
To further agree with this, when my kit was stolen and I had to replace quickly I picked up a 5d3, a 70-200 2.8 I (not the 2 for cost saving) 24-70 2.8 II and a 50 1.4 (tho a 1.8 would also work). I find that while the 24-70 is an awesome lens, I still swap out to the 50 a fair amount....so the concept of a 700-200 + a 40 2.8 is not a bad starting place.
If I am honest, if I thought it would be some time before I could get the second of the two main bits of glass I would still consider the 23-105 4 + 70-200 2.8 with a 50 1.4/8 for very low light...but remember the 5d is a fighter in low light so do not be too afraid of F4 as a get-you-by-lens. In fact I know of a well respected wedding photog who only shoots jpg on a 5d2 with the 24-105 4 and gets some great wedding coverage.
Good kit helps, good skills are better.