In the short term, until enhancements like 38262 Outline view (née 3959 under OO) are taken seriously I very much doubt that office's core market of document creators will be threatened by LibreOffice.

For casual/light consumers of office documents, however, I think that Libre/Open office has very much arrived. I'm starting to see it in the default-install on my customers' machines.

In the longer term perhaps that will prove to be the thin end of the wedge.