You misunderstand the problem. It's not an issue that the project is decades long, it's that it is going to take, say 50 years of capital- and carbon-intensive development to solve a small part of a larger problem that we only have, say, 50 years to solve. And it offers virtually nothing over EVs except to gratify some anti-car ideologues.

NOTE: if it's not evident, those 50 year figures are made up. The point is that we have limited time and resources to solve the whole climate problem and we should be efficient (rather than ideological) in our approach.