There hasn't been any reliable news on the development of EX4 since the movie was semi-officially announced for a release in 2017, raising doubts in the viability of the fourth installment. The doubts were further reinforced when Stallone himself made a statement that an EX4 would be "Stallone-less" if it was to move ahead. Plus he seems to be involved in the Guardians of the Galaxy 2, and actively searching for dramatic roles, distancing himself from action movies. That being said, not winning his Oscar might have changed things.
Now 2 more or less reliable pieces of news have surfaced over the past few days giving some more life to the viability of an eventual EX4.
Randy Couture has confirmed to The Arnold Fans that filming on The Expendables 4 will get underway in the fall.
At the #ArnoldSportsFestival, Randy Couture confirms Expendables 4 starts filming this fall! #schwarzenegger
Yibada is reporting that Li Bingbing will appear in the sequel and according to the American based Chinese outlet, after the delays because of the script changes, the movie will finally start filming in May! The outlet further reports that while in Australia, Li said she got sick out of worrying she might not be able to do "The Expendables 4" because of a barrier.
Not sure how reliable all of this is, but if true more news should surface soon.