Teclast has announced on its Weibo account:
#台电X98 3G#，将于5月份正式首发升级微软Win8.1体验版固件，全国领先！升级后的X98 3G拥有强大的办公能力。最快64位英特尔Bay Trail-T处理器X超级板强大的硬件，让你玩转Windows和Android两个系统。敬请期待Win8.1固件！
Which Google Translate renders as:
# Taipower X98 3G #, will officially debut in May Microsoft Win8.1 experience upgrade the firmware version, the nation’s leading! X98 3G has a strong ability to work after the upgrade. The fastest 64-bit Intel Bay Trail-T processor board X super powerful hardware, so you Fun Windows and Android both systems. Stay tuned Win8.1 firmware!
1Pad has an item about this [Google Translate].
The key question is whether the 32GBs of internal storage in the X98 3G will leave any space for applications and if this will turn the tablet into a dual-boot system.
It will also remain to be seen if people outside of China will be able to buy this new firmware. If all of the instructions are in Chinese, someone better post a translation. In addition, can Teclast even sell it to people outside of China? Geo-restrictions might apply. If you want to buy this — or the Onda V975i or Onda V819i — because of the possibility of Windows, wait until all details are known.
Previously here:
Teclast X98 3G Gets A Review
Teclast X98 3G Android Tablet Running Windows 8.1
Teclast Announces New Retina Tablets
Mike Cane’s xBlog 
Is tomorrow the day of the upgrade?
It will be finally dual-boot?
No word yet. So far, everyone is saying it’ll be June for all tablets. We’ll see.