Does SQL Server Management Studio 2017 Contain a New Explain Feature
No, not a feature - it's turning one of these on:

SET SHOWPLAN_TEXT ON;  
SET STATISTICS PROFILE ON;


The SHOWPLAN_TEXT option and STATISTICS PROFILE option are well-documented and have been around for over a decade, but I don't know when SSMS started turning it on for the combo of live query plans and actual plans. I would consider it a bug.

Here's the SSMS bug I filed for it.