Well, the Tsar Bomba was made as a single of a kind, ust for testing, and at half of its designed size because a bomb of that size is basically useless.

So I don't think we would get larger warheads. It's more likely we would get smaller ones, at power levels that can be used, and use their small weight as a feature. (Not something great, but I don't think we will ever use an Earth Crust removing bomb.)