We give a short overview of existing branching fraction measurements of charmless semileptonic $B$ meson decays of the form $B \to X_u \ell \nu$, with $X_u$ being $\pi,~\rho,~\omega,~\eta$ or $\eta'$. We focus on results from Belle and BaBar collaborations. We report prospects for measurements and estimates for $\vert V_{ub} \vert$ determinations in $B \to \pi \ell \nu$ decays at Belle II. With the full expected Belle II dataset, $50~{\rm ab}^{-1}$ of integrated luminosity, the estimated errors on $\vert V_{ub} \vert$, including expected improvements in Lattice QCD calculations in the next decade, are $1.7~\%$ and $1.3~\%$ obtained with the tagged and untagged method of companion $B$ meson reconstruction, respectively.