I received this from Toyota this afternoon in response to my query.:
"Thank you for contacting Toyota Motor Sales, U.S.A., Inc.
We appreciate you taking time to e-mail us with your inquiry.
Toyota does not have any restrictions on the use of a weight distributing hitch for towing a small travel trailer. We do apologize as there is no literature available which prohibits the use of this component.
Your email has been documented at our National Headquarters. If we can be of further assistance, please feel free to contact us.
Sincerely,
Erik A.
Toyota Customer Experience Center"
" Customer By Web Form 03/06/2017 08:16 PM
I have a 2016 4Runner Limited. I occasionally tow a small travel trailer and use a weight distributing hitch. The owner's manual is silent on using one of these weight distributing hitches. The total tongue weight and trailer weights are all within the specs in my owners manual.
Is it permissible??"
Clearly, this is different information than was given to Speakeasy a few years ago. In any case, I hope this helps to put the matter to rest regarding WDH use on the current generation of 4Runners.
Greg