Thank you for the suggestion Arty, but that shows I hadn't described the goal correctly

1. Indeed there is no need for HDR in timelapses.
2. Autoexposure may work in some cases but in many cases it won't. Chances are obstacles, movement, birds, or whatever can cause the camera to "jump" more or less EVs and spoil a complete shoot.
What timelpasers wish for is a device that would allow to start a shoot say 1 hour before sunset and end 1 hour after sunset. During that time take an image every 3 seconds but change exposure values (let's say from -3 EV to +3 EV just as an example) consecutively but in increments of 1/32 EV to avoid any flicker in the final film. (20 pics/min = 1200/hour = 2400 images total with varying EV from -3 to +3 in 192 steps)
Of course one would have to find out the correct settings by some experiments but at least one would get a predictable and a flickerfree result.
Right now there are just some DIY approaches from people using motorised rigs to turn the aperture ring very, very slowly.
Best
Jürgen