The latest information shows that Sony is actively working to implement 8K videos for the upcoming mirrorless cameras.  According to this, the cameras that are likely to have 8K video in the near future are Sony A9 II, A7S III and A7R IV.

Considering these high video rates at the moment, Sony is only competing with Panasonic in the industry. Panasonic is the only manufacturer among mirrorless cameras offers true 4K in 4:2:2 and 10-bit.

We already know that Sony is rumored to announce two new sensors. One of the Sony full frame sensor will be capable of 60 megapixel stills, 16 channels, and 8K video recording. The other one is 36MP. This means we might see the 60MP sensor on the Sony A7R IV and 36MP BSI stacked sensor on the Sony A7S III or A9 II.
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https://www.dailycameranews.com/2018/12/sony-a9-ii-a7s-iii-and-a7r-iv-to-feature-8k-video/