According to these links, Yotaphone 3+ has almost the same hardware as Yotaphone 3, but it can freely screen any app on the Eink screen instead of forcing you to use their build-in apps like Yotaphone 3. The Android version is 8.1 Oreo.
https://qooah.com/2018/08/08/yota-3-plus-in-hk/ (sorry it's not in English)
https://1review2day.com/new-model-yo...us-introduced/
I also saw a reply from the Yotaphone company (Chinese) on Reddit. The Yotaphone guy says Yotaphone 3+ will be distributed from a Hong Kong company. They're currently looking for more distributors.
https://www.reddit.com/r/YotaPhone/c...n_information/