I thought about this a little bit more as it's been a while, but I think the reason Office is so dominant is that it's really 5 different pieces of very different complicated software. It's easy to knock off Word, but to copy Word, Excel, Powerpoint and make them all great, and compatible is very difficult.

I think if you separated them and chose the best alternative word processor and best alternative spreadsheet and best alternative presentation software, maybe you would have a better shot at replacing them. WPSOffice has the best excel, but powerpoint isn't as good, etc.