Hello,
Okay, now I understand why this feature request is still pending on the official ACF forum. The problem come from the fact that fields conditional logic don’t use Ajax, so choices cannot be loaded dynamically (example: render all terms in the select box).
A workaround would be to let the user enter a term ID manually, or term slugs, but that would leave some spaces for input errors and won’t be very “readable”.
I know that ACF developer has plans to rework the conditional logic, and he will most probably give necessary tools to achieve this sort of advanced conditional logic.
Note: In your screenshot, you’re talking about “Taxonomy Terms” field, which is a new field introduced by ACF Extended.
TBH, I’m overwhelmed with feature requests, so I cannnot guarantee that I can take a look at it before the release of the new conditional logic feature. If I work on it right now, I also takes the risk to have to rework it later in order to make it compatible with the system, something I would like to avoid if possible.
Regards.