Interesting... color me skeptical.
This could be good, or it could be very bad.
First, there is an issue of teaching current workers new skills and balance that against bench time. ( Bench time is time when a consultant/contractor is not billable, but still collects a salary. )
But then when you think about it... suppose you have a guy who's an expert at X. If he rotates to a new client, so he can learn Y, does he still get charged out at the same rate as being an expert at X? In this case, you're over billing the customer for a sub par resource. An example could be that you take an Oracle DBA who has 15 years of RDBMS skills and send him to an account where they need someone who knows NoSQL object stores. Here he's a novice, and the client is paying him to know something where he is clearly learning on the job at their expense.
Then there's the other issue... What happens if you have this guy Bob, who's got 20+ years in at IBM and its his time to rotate out to a new client. Only there's no job for him to rotate to? What happens then? Can he be made redundant?
This is a bit of a double edged sword. On the one hand... it forces older employees to learn new skills rather than be comfortable staying within their niche. (Humans, for the most part, are not comfortable with change.) On the other, it makes stealth firings, or demotions easier.
And one other consideration. Suppose you live in NYC, have a family and everyone is settled. IBM now says congrats, you're on a new project in Cleveland, OH and you have to relocate. Refusal to relocate means grounds for termination. If your family is settled... relocating every 2 years, assuming that IBM is going to cover all of the costs... is still going to be a deal breaker for the older employees. (Try buying and selling homes every 2 years....) (Assuming you can't find another project in your current area. ) Try telling your wife and kids that they have to move to a new school. No, its not a promotion or getting your ticket punched... but just for the same old job and salary.
This still would work for the younger employee who rents an apartment and doesn't own a house, or have a family to uproot.
The other issue.... regional salary differences... If you move from NYC to most of the mid-West, your cost of living goes down so if you're being paid $$$$, you win. However the reverse... you go from lower cost of living to higher cost of living... you're getting screwed.
So many issues with this less than thought out plan... not good. The Devil is in the details and IBM doesn't do well when it comes to specifics...