New insulation technology changes the balance. Practical aerogel production means that heavy, shape-constrained high-pressure tankage is no longer needed, so that tanks may now be light and have the most convenient shape.

Furthermore, recent advances in catalysts for hydrolysis, some directly from sun exposure with no detour through electric form, make production of hydrogen from water and light practical.

New airframes with lifting-body designs, already better than those used now, have more room for tankage as a side benefit.

The practicality of any idea can change very, very rapidly, as details of solutions to engineering problems change. Recently solar and wind power were impractical. Now they are cheapest, and coal-fired power is impractical.