[Gibbon1]

Hybrids are interesting because you can reach higher bypass ratio's because you can power n number of ducted fans off m engines.

Currently increasing fan sizes are getting problematic. That is the problem with the 737 MAX. The fan diameter of the new engines is too large to fit between the bottom of the wing and the ground. So it had to be mounted forward and up which fucked up the aerodynamics.

Two other advantages are, potentially maintaining thrust in an engine out situation. When you lose an engine not only do you lose half your power but the thrust is unbalanced. And faster throttle response. Turbine lag is a big issue with jetliners.

Note: The reasoning behind high bypass turbofans is thrust is proportional to delta v times the mass flow rate. Where power input is proportional to delta v squared. Bigger the fan the more efficient you are and the less fuel you use.

Diesel is kinda interesting. Manufactures are developing diesel engines for light aviation. I suppose you could have a hybrid diesel/electric aircraft.