Hi Manu,
The latest release of the U2 Common Clients (v5.2.1) includes UniObjects for .NET with .NET Standard 2.0.
U2 Toolkit for .NET is on the roadmap for late this year. We will be implementing .NET Standard 2.0 which is included in .NET Core and .NET Framework. I do not have a definitive date at this time however we are targeting the 4th quarter of this year.