There was an article in one of the magazines (I think Flyer) about a year ago where they did the calculation for a two-seater. From memory, a Twister. Based on the latest technology, particularly battery, they calculated that they could rip out all the fossile fuel stuff, add in electric motors, controllers and so forth, and fit sufficient batteries in the aircraft, remaining within MTOW, for 40 minutes of flight. And they made some very generous assumptions to get to that number anyway. So, not enough for any meaningful x-country plus VFR reserves. Battery technology has to improve dramatically for this to work.
Gliders need only a few minutes of power to get to a height sufficiently for thermaling. I'd never heard of that Moni, but that sounds like a fair application.
As far as hybrids are concerned, well, they're nice for stop-and-go traffic, where kinetic energy can be converted into electricity and stored in the battery when the lights turn red, to become available again when the lights turn green. But this is not a typical usage scenario in an aircraft. Aircraft typically need continuous power and converting/storing that in an intermediate form is going to lead to efficiency losses in any case, and weight addition for no gain. If you want to use a light-weight turbine APU, just run the electric power from that APU directly to the propellor motor. Or even better, connect the propellor directly to the APU shaft.