There should be an option to have effects crescendo, meaning getting more intense over a period of time. I would especially like to see this applicable to pitching.
You can approximate this process by opening two identical versions of your track, one over the other. Apply the full effect to one track. Now fade from the “clean” track to the effected one.
File > Export to a WAV or other file type and Audacity should mix down the two tracks into a permanent single track with the crescendo burned in.
Fair warning you should be using WAV or Audacity Projects for this. MP3 files degrade in quality as you do effects and editing with them.
Another note: Nobody is going to program that into Audacity because of the two or three people who need it. This is a science fiction production effect, not something people are going to need every day and twice on Sunday.