The medical insurance industry especially HMOs. have been pushing this for decades. Maggie Thatcher started a lot of this, then we had NICE. EBM is being pushed from multiple sources, and a huge one is medical management with a focus to contain costs. Its not surprising that a major public health measure like the Affordable Care Act has this clause. It is however a problem in that the processes the IOM are using for things like this are still under development.
The emphasis on EBM has good intentions in its broadest sense. The sense in which medical treatment is limited to only some things and not others, based only on EBM, is a huge problem. In theory doctors still have independence, as EBM guidelines are only advisory, however in practice these guidelines are coming to be treated as hard rules. HMOs certainly treat guidelines that way.
In organizations with a primary focus of making money, whether that is a private hospital or government looking to minimize its profile, or an HMO, they will naturally want to use such guidelines. Further there have been moves going back at least a decade to provide legal protections and avoid lawsuits, at least in some countries including Australia and England.
What this means is that there may be a degree of support for the IOM position from the Democrats and the Obama administration. This isn't a surprise to some, but I think it is in part an unintended consequence, and further that they may be vulnerable on this point. However the typical response is to go defensive, and we see an example of this in the Conservative coalition in the UK over ATOS/DWP.
In the UK they deny, and defuse, and point the blame elsewhere. They publish invalid statistics as well. I am not convinced this will be as easy to do in the US as the UK has much less transparency than the US, though that is changing fast.