Handling of duplicate ideas has been a very tricky thing. The way we solve this is by promoting multiple ideas to the same feature, making the feature a kind of 'control point' where all of the ideas come together.
The problem is that this introduces a lot of manual labour to keep fields in the feature up to date against the fields in the idea - namely tags and custom fields that we use (customer asking is the biggest one)
Select a set of fields in the idea that map to fields in the feature
whenever a new idea is promoted to an existing feature, this subset of fields would be added to the fields in the feature
Create an automation that is triggered by 'when an idea is promoted to a feature'
Add values from field X in the idea to field Y in the feature
This would reduce a HUGE amount of manual work that currently goes into keeping these fields up to date