I want to say you're correct in that they confirmed that last July. Though I wonder if they'll split Part 3 into 2 seasons like in Japan or keep it to one release. I hope Part 4 is kept into one release as well & not split into three 13 episode releases.
I don't think there is any doubt that the longer parts will be broken into 13 episode chunks.
the only new release that I know of in recent memory that wasn't broken up into parts was my love story by sentai, and it was originally planned to be but because of some sort of delay they decided to just release it as a full set.
for the heck of it though...
*looks at viz releases by release date
http://www.rightstufanime.com/category/Blu~ray,DVD/publisher/VIZ?order=custitem_rs_release_date:desc *
pokemon advanced is a collection release
sailor moon crystal is being broken up into chunks
sailor moon releases in general are more than 13 episode chunks but they are an odd mix of both a re-release but also a new release since it has a new dub and no censorship so is likely an exception than something to base anything off of.
*keeps going and gets to a conclusion*
I think we will really just have to wait and see as basically jojo will be the first series with less than 30+ episodes per part that viz will have released in a very long time. they mostly just release endless series like naruto and pokemon anymore and have some really weird license rescues like moribito (which was originally anime works apparently but is now viz)
but going off sentai and funimation I would expect each season to be broken up into around 13 episode chunks.