  CP-violating asymmetries in $B \to \pi \pi$ and $B \to \rho \rho$ decays can
help specify the weak phase $\phi_2 = \alpha$ of the Cabibbo-Kobayashi-%
Maskawa (CKM) matrix. We discuss the impact of improved measurements of these
processes such as will be available in the near future, finding special value
in better measurement of the time-dependent CP violation parameter $S_{00}$ in
$B^0 \to \pi^0 \pi^0$ and $B^0 \to \rho^0 \rho^0$. Reducing the errors on $B
\to \rho \rho$ measurements by a factor of two can potentially lead to an error
in $\phi_2 = \alpha$ just above $2^\circ$, at which level isospin-breaking
corrections must be considered.
