Their business is designed around tearing out margins in the value chain, and passing the savings along to customers. It's a business strategy unheard of - not only do they pass on a lot of savings, they force vendors to do so as well.
The healthcare system is completely fat with gristle, exactly what we need is a Walmart barking up the long-tail.
$15K-$20K for setting a broke arm? I don't think so. $30 for the Aspirin while you're at it? No. $2K for the scan? No goddam way.
Walmart would probably only get into things that could be 'very well operationalised' ie more common stuff.
And consider the vicious leverage they would have over drug makers ...
Healthcare is 15% of the economy and growing, Walmart tearing into Healthcare would be more transformative that the existence of Google.
For any service that Walmart provided, I would be glad to go there.