If hydrogen busses really were going to have a lower operational cost per mile in 2050, then some company would be offering to lease busses for $X per mile to transit operators, fuel included, for a 25 year lease. They'd make a loss initially, but big profits later.

That approach turns this technology maturation and cost risk into a market, and those with most expertise can then put their own money on the line to help everyone make the right decision.