Many people have fiber now. If it could delegate task fragments based on connection speeds it might be efficient enough for reasonably fast results. I think enough people would choose this over the alternative even if it means slightly slower results. But too much of a disparity and I could see people rejecting it in exchange for what might be percieved as the "premium" experience of the corporate models.
The big irony is that if the centralized AIs get good enough, they could in theory create the dectralzied model themselves, and may infact see it as a means of self preservation, if AI actually ever gets to that level of intelligence.
I'd even say an advanced enough AI may eventually do this with all available computer power connected to the web whether we want it to or not at this rate.