I would love to see a better MIDI Mapping in Reaper. That would be great to have some kind of MIDI Map manager/table similar to Ableton in which we could enter a Min and Max value for each parameter we want to control. Until now I am using the Parameter Modulation to scale MIDI CC with VST parameters but it is not very intuitive or even accurate. I found a plugin called Realearn (
https://www.helgoboss.org/projects/realearn/) which is somewhat helping a bit but it's not perfect either.