We can switch to hydrogen for lots of stuff that requires carrying your fuel on your back, but some things get tougher because the density is just not the same as a hydrocarbon.

These are all surmountable (biodiesel, carbon capture->fuel cycles, bioreactors, etc), but they take time and money.

In the end, what will push us to get there are economic shocks. We're getting there, it's just painful.