I know, this topic already was discussed a lot, but not in the community and I just heard it again :-)
It would be great if Pipedrive had custom fields which are only shown when a certain value is in another field. With this feature you would have a lot of opportunities: Different Lead Qualification Criteria according to the size of a company or for different products. Regional specifications like tax requirements.
If you are going all the way, you would allow dependencies for custom fields depending on the pipeline or phases.