After finally integrating the picture-in-picture feature into its platform, YouTube is currently experimenting with the new zooming feature!

It is reported that some premium subscribers can now zoom in with a pinch gesture to get a closer look at a specific section of the video. You can zoom in up to 8x. Furthermore, because the feature is still in its early stages, it is only available to be tested out by the Premium subscribers.
To try it out, go to the Settings Menu and look for the “Try new features” section, which will appear for Premium subscribers. This can be done whether you open YouTube through your phone or website.
Pinch-to-zoom is available to try until September 1 in order to give some time for YouTube to gather user feedback and work on improving the functionality before rolling it out more widely. Following that, the video platform may either officially launch the feature or reveal a later launch date (if there are any issues with the functionality). Unfortunately, there is no word on whether the feature will also be available to non-paying users.
Zooming in on a video can be a feature that others might anticipate and also something that may be deemed insignificant to some users. Be that as it may, seems like Youtube is planning to introduce this feature on its platform soon.
Source: The Verge, gsmarena