Wait for Reliability Data
The biggest reason to wait and not buy the 16-inch MacBook Pro today is to see how it holds up long term. This does mean waiting into 2020, but you may be thankful if problems appear.
Apple switched the keyboard mechanism completely and so far it is not part of the keyboard replacement program like every other MacBook for the last few years, but it is still a new device.
Wait and see if the keyboard holds up well and if there are any other issues from the new design before you buy the new MacBook Pro.