Best technology for coal electricity capture costs $10/watt (close to new on budget nuclear plants), and only captures 65% of emissions. A better “free” climate strategy would be to put them in “backup peaker” mode for renewables and run them at far less than 35% of year.
DAC can work only if price of carbon is $300/ton ($3/gallon gasoline). Still, 100% renewables is cheapest path to avoiding those taxes, but afterwards, DAC can hope to pay for itself.
For aviation, LH2 is best because the tanks are very light too, and much of the fuel is used on takeoff which has a cooling effect on the remaining fuel. Cruising at matched boil off rate works well, and there should be enough pressure resilience for reserve fuel. Small battery can also help with takeoff and regen to handle aborted landings, as well as manage with boil off rate.
A technical challenge is dealing with very cold/liquid H2 in the fuel cell, and pipes. Unclear if that is worked out yet.