alt Hacker NewsI don't know about that... unless a good open-source option comes out for corporate email that matches what Outlook/Exchange/M365 offers for calendars and scheduling.
That last part is the real point of integration... then real time chat and messaging status baked in... it's hard to beat. You have services and applications that offer pieces, but none integrate as well.
In the early 2010's I think that both Blackberry and Mozilla had an opportunity to create their own competition in the space and neither did. Google is pretty close, but IMO still a much lesser experience, reinventing a new chat app every other year didn't help their cause at all.
Google seems most likely to capitalize. GSuite is standard practice even among many large companies provided they were founded in the past ~15 years and aren't on the Microsoft teat. Their search is also _so much_ better than Outlook that it's even more useful as a forever-store.