HR managed services are certainly one big opportunity here as are leveraging Microsoft's B2B connections - however those are just the layer of utility services they can build over a massive 'corporate directory + network' and a feed. The opening up of that directory across companies could be huge and expand the potential competition to far more than just Oracle, Salesforce and IBM (to things like FB for Work, Slack etc.)

More thoughts on that here: https://medium.com/@ux/will-linkedin-and-microsofts-new-play...