This recent article
http://www.motorsport.com/indycar/ne...for-19-844234/ is quite intersting. Mark Miles talked to journalist David Malsher and confirmed ongoing discussions with Portland, among other things.
A possible street circuit in Calgary, Canada, also gets mentioned in the article. Still, no further US venues have been written about.
Personally, I feel that's kind of sad because I still miss Milwaukee, and I guess other fans do so as well.
Regarding Mexico, Miles said that there are no discussions between Mexico City and IndyCar. However, "there are other conversations about a Mexican venue but I don’t think they will be viable as early as 2018,” he is quoted.
In relation to this, the article mentions a 1 and 1/4 mile flat oval that is part of Autodromo Miguel Abed at Puebla which does not have a SAFER barrier yet.
To be honest, I wasn't even aware there is an oval in Puebla.
Miles also says IndyCar would be open to a return to Australia for its season opener "if all the elements could be put together".