Libre Office and Only Office are the only real MS alternatives (which offer decent compatibility) at the moment but I'm excited for KDE expanding its own suite of software, which is something that GNOME has had over it for a long time now.
Expanding? Calligra/KOffice predates LibreOffice/OpenOffice, it just lost on mind share because the Gnome fanatics hate anything KDE more than the messiest OpenOffice spaghetti code.
I hope it picks up with improved KDE popularity recently!
No, sadly it won't. Its time is over. There was a window of opportunity when Calligra's good separation of UI and logic would have made it a good foundation for a web office suite and the desktop version would have benefitted as a side effect. That niche as been taken over by OnlyOffice. I fear its future lies in being a plugin for document viewer Okular.