I wouldn't write a publisher acquisition for Sony off the table just yet. Between PlayStation Productions, PlayStation Plus, and PC ports, Sony has a lot of ways to leverage content libraries from midsized publishers like Square, Capcom, Ubisoft, etc. The unlikely options are massive publishers like Take Two, EA, Bandai Namco. Sony have said they are willing to allocate more funds if necessary, but the question will remain if the acquisition is worth it.
I definitely wouldn't write anything off.
But I don't feel like buying a publisher is Sony's priority. I think the biggest reason why Sony would, would be more so to prevent someone else from acquiring their partners. Especially something like Final Fantasy being acquired by Microsoft. (I think chances are good, MS will either acquire a Japanese publisher or at the very least will acquire several Japanese developers. Variety is an important aspect of their current business model.)
I think Sony has been pretty content with buying smaller developers and raising them up that way. For a tiny, tiny fraction of what some of these publishers cost, Sony has gotten some great development teams. Insomniac Games was an insanely good deal. Activision is costing 305 times what Insomniac Games cost. I think it's hard to deny the value they've gotten from buying studios full of talented people.
But I won't be surprised if that changes.