Yes, the Ubuntu Touch OTA-4 may be rescheduled again, because there are some problems with the language pack generation mechanisms.
This is what Canonical’s Łukasz Zemczak posted in the mailing lists yesterday:
“Sadly the OTA-4 release might be once again a bit delayed. We noticed issues with our language pack generation mechanisms which do not seem to be working for our stable overlay PPA,”
OTA 4 will switch the system’s code to Ubuntu 15.04 Vivid Vervet and will bring a huge list of features including support for dualSIM, browser improvements, support for USB Tethering and NFC, support for M3U playlists and support for video playback under the lockscreen will been added, among others. But we have already covered the highlights of Ubuntu Touch OTA-4 Update.
As a reminder, Ubuntu Touch is used by default on Bq Aquaris E4.5 Ubuntu Edition, Bq Aquaris E5 HD Ubuntu Edition (which can be ordered starting with today) and Meizu MX4 Ubuntu, a phone that is available only in China, for now. Also, Canonical provides official support for the Nexus 4 smartphone, developed by Google and LG.