If something cannot exist at the pressures found on the upper levels, it wil not be found there. But who said that the "sea" must be metallic? You can have liquid hydrogen at 7 bar and 30 Kelvin, for example. If there is any place in Jupiter where the pressure is 7 bar, the temperature is 30 Kelvin, and the dominant stuff is hydrogen, a liquid surface will be found there.

Personally, I do not think that this combination of conditions can be found anywhere on Jupiter. But perhaps one can find it on Neptune.

By the way, a state diagram is just that: a diagram. There is nothing to prevent us from extending it to the gigabar range, the megaKelvin range, or both. We may not know exactly what to put inside these far part of the diagram, as it may not be possible to compute this from first principles, but there is nothing conceptually wrong with the idea that even the core of Jupiter is to be described by a state diagram.

In fact we might be able to explore the further regions of the hydrogen state diagram by sending probes inside Jupiter.