I think, at least in nearest future, there is no risk - simply all this activity is hanging on very generous assumptions related to battery development. So far no signs of real breakthrough in this area. NASA is expecting in next 5 years increase in battery capacity around 10-15%. To make EVTOL working idea is needed increase at least 500-1000%. I'm expecting that within next 2-3 years founds on EVTOL's will be drastically reduced.