Gimp has a morph feature which can be used to create pictures in between two frames. If you want to double your render speed you just have to drop every second frame off which can be done through video sequence editor: Press n and set the strobe from 1 to 2. Of course that is just a part of the solution. Then you can use Gimp to morph those missing frames. Unfortunately that has to be done manually. My request is that some developers would find
this useful method to get animations in decreased time and create a method to do this automatically so that all you have to do is just taking care of settings, like “from x to y”.
Perhaps it would be worth consulting with Gimp developers to have such an automated feature either in Gimp or in Blender.
What do you think?