When will windows phone 10 support EWS?

EWS is Exchange Web Services and since at least 5 years supported by Linux, iOS, OSX, Symbian, and every single other operating system and product vendor worldwide. It's a standard by Microsoft.

Only Problem is, Microsoft themselves don't support it. Microsoft makes it thus virtually impossible to use windows phone on a professional or business level. As it's needed to organize contacts into groups / sub-folders.

It's very weird, that Microsoft doesn't support EWS and thus officially states it doesn't want business and professional customers where Apple and other companies are saying: yes, sure we support this feature which is a must have for professional and business customers. Why would we refuse professional and business customers? They bring good money into the basket!

But MS keeps repeating: no, customers who pay damn good we don't want! We will not support anything for the professional and business community. We don't want their money. Go away!

I wonder why MS does that?

I think you're asking the wrong question here. I think the more correct question is "When will Exchange ActiveSync support Outlook Groups".

I would ask that question in a more relevant community.

Try here for starters

https://community.office365.com/en-us/f/158

Exchange Web Services .NET by Independentsoft supports Windows Phone and other platforms (.NET Framework, Mono, Xamarin, .NET Core)

/Miki