Dangerous because high current high voltage DC is like wiring up your house to an arc welder! Many burnt out mill sites would confirm. My 1880 installation still works OK to heat water for my shower and run a few light bulbs, but it is useless for anything else.
Heat is what we need, so a 1500 litre AKVATERM heat store with two immersion heaters, and woodstove boiler is the current plan. If the hydro setup is correctly sized the winter flows should average 6kw of nominally 240 volts AC electricity. Both the frequency and voltage variations are not important since the power is used only for heating. Summer flow can drop to below 2kw, and really cold winters without rain (like last year) can reduce our river flow to summer levels. So two or possibly three immersion heaters can be swopped around to provide a suitable load for whatever power the water wheel is producing.
I guess some regulation is needed and my near neighbour has a load control setup on his 8kw cross-flow turbine. The turbine always runs at near full power, and the power is switched to various loads throughout his house. Not being an expert on electronic controllers the black box that does this is magic to me, but it certainly works well.