This feature request is still working its way through the backlog queue.
Thank you for your patience. We are thrilled to that replying to a chat message in the desktop client is now available as part of our Public Preview. It is expected to roll out to the public ring over the next several weeks.
For details on switching to the Microsoft Teams Public Preview version, please see : https://aka.ms/TeamsPublicPreview.
We look forward to your preview feedback!
The team has delivered improvements to the New Meeting experience in Calendar such as optional attendees, richer custom recurrence UX, as well as enhanced meeting RSVPs.
To learn more about RSVPing to meetings in the Teams Calendar, how to create a recurring meeting, and the new meeting scheduling experience including the scheduling assistant, please visit https://support.microsoft.com/office/schedule-a-meeting-in-teams-943507a9-8583-4c58-b5d2-8ec8265e04e5.