I'd argue that Microsoft and Amazon's branches were at least tangential to what they were doing in the back-end and that they already have most of the required talents to do it right.
I have no idea how Intel could work their way into running an app store beyond "we have tech and market dudes, good enough right?"
With their new fabric/modular system, the modules are effectively "apps". Though possibly sold by app developers, you could install the Adobe module or the Autodesk module and it would have hardware/ram/storage tuned to those applications. It will start with DL and Graphics accelerators but then morph into application specific.
I have no idea how Intel could work their way into running an app store beyond "we have tech and market dudes, good enough right?"