"sending activity history to Microsoft's servers"
And here we go again. This brave new world in the making obviously considers that everyone wants to sync everything and show it to everyone by default and, to do so, Microsoft is one more in the long line of application writers that wants to store all your data "to better serve your interests".
Timeline. Hmm, where did I already hear about that ? Oh, right, Facebook. That thing that is platform-independent. And not everyone was happy with it at the time.
So, Microsoft, with Meltdown and co on the loose, you want to implement a server-held repository of everything a user does and push it out on whatever thing the user is using at the moment. Brilliant. No security concern there, for sure. No privacy concern either, right ? But, it's nothing important, you say ?
Then why do it ?
You are going to include a shutoff key for that, right ? And not make it on by default ? Yeah, right. And I'm winning the lottery tonight.