pH of dilute acids in hexane
pH is defined for water solutions; using it elsewhere is either impossible or leads to contradictory results like yours. Who said pH should not be too high? Well, you might argue that high pH implies alkaline solution, does it not? No, it doesn't. Alkaline solutions are (roughly speaking) those with high concentration of $\ce{OH-}$. In water this means the same thing, because $\ce{[H+]\cdot[OH-]=10^{-14}}$, so low $\ce{[H+]}$ means high $\ce{[OH-]}$ and vice versa. In hexane, not really.

To determine pKa values which are way beyond the physically possible range of pH, we extend it with things like Hammet's $H_0$, and thus build a ladder of measures suitable for a much wider range. You may call it "effective pH" or like that, but remember: it has little to do with literal concentration of $\ce{H+}$, and your hypothetical solution of $\ce{10^{-30}M\; HCl}$ in hexane is in fact neither acidic nor basic.