Be careful, all I2S aren't wired the same and don't have same connectors. I2S was originally designed for inside components, allowing the designer to ensure matching. Whatever you're considering, please first check w/manufs that they'll be compatible.
FWIW, I think Denafrips has a converter like you're describing. I'd ask Alvin. BTW, the new Terminator2 has 3 different I2S connections for this very reason. Cheers,
Spencer