Currently you can link CTA to a timeline entry however for reporting purpose I can not measure or see how many timeline entries were written per CTA.
We use timeline entries to help us measure the success of our CTAs as well as activities generated from out CTA.
Current process is to create a data designer which is not fun. If we had a look up value with the Timeline object that looks up to CTAs.
The same would apply for success plans, we do not always have a visibility to the success plans within the timeline object.