Follow the money. Advocates claim that the price of gasoline makes state of the art hydrogen technology competitive now; this then is an issue of scaling up the concepts. Transportation and transfer systems need to be designed. Transitional technologies like wind generators will pay the fossil fuel price to change.
Next, any hydrocarbon can be used to produce hydrogen. Wood, grass, pine tar, garbage, plastics, any C-H can in principle yield an H. There are many approaches considered to these and many other source options. We are not only talking about solar and wind. But, both of these have also made great strides. The final solution will likely be a hybrid of many technologies applied where each is most appropriate. Of course coal and oil are also great sources of hydrogen. But the key is a hydrogen base. IMNSHO.
Also, one key concept is decentralization. We already see this idea succeeding in the use of farmer produced ethanol for use on the farm. The last time that I checked, this practice is growing at a startup rate of 5 to 10 X per year in the US. The farmers appear to find this process more than competitive with gasoline and diesel oil.
Some minor edits plus one more observation:
Fusion power translates directly as a potential source for H2 production; for transit systems and industrial equipment. These two goals - the strive for fusion and an H2 economy - are compatible.