It is not clear whether existing airframes can be retrofitted to burn hydrogen. There is not room in the wings for LH2 fuel because, despite its extreme mass-energy density, it takes up much more space. Carrying it inboard on passenger flights might be seen as a safety hazard. Most likely, LH2 would be carried in nacelles slung under the wings alongside the engines.
New airframes may use fuel cells to drive electric turbines in preference to burning H2 the ordinary way.
Once LH2-fueled craft enter a route, kerosene craft will be unable to compete there, because the lighter fuel load allows for more paying cargo in its place.
Major airports will electrolyse H2 from water on-site, and bank LH2 in underground tanks. A big airport will have huge solar and wind farms around it, feeding in power for that. They will represent a very substantial part of each nation's generating capacity, and the LH2 much of its storage.
In the nearer term, there will be a massive demand for synthetic kerosene for the current fleet.