Sodium Ion is a real game changer. But I doubt it will compete with Lithium Ion on energy density anytime soon.
But that's not necessary to make major changes in the power grid. Solar and wind is already cheapest form of energy generation even considering the expense of Lithium to store the energy when renewables aren't generating. If you're just installing stationary battery banks, you don't care that much about the energy density as you would for a battery in a car or phone. Set up banks of cheap sodium ion batteries strategically and not only do you have plenty of power stored for when it's not sunny or windy, you may avoid widespread power outages when power lines are downed.
