Honestly, Linkedin by itself would have made a very strong Salesforce competitor. Not sure why they never went down that route, instead they focused only on recruiting, the least interesting use-case.
The complete rumor I have heard over the years was a gentleman's agreement between CRM & LKND
Seems like this is what they're going for - https://ncmedia.azureedge.net/ncmedia/2016/06/msft_announce_...
Step 3 is you get an email (marketing or sales) because Dynamics notified assigned a task to a sales rep or started a job in marketing automation.
Then, based on you opening/ replying/ not opening the email, a whole new series of tasks are created.
If MSFT / Dynamics do this right, they will have a very strong Salesforce competitor.