Temporally ban new idea from entering and escaping the community.
(call it a travel ban, or a global freeze, whatever)
Why ? Because at first review the existing ideas (Duplicates + Active), and then please decide them as Planned / In Review or at least Disapproved if they were no future use.
This will guide users and Tableau team to align on same page and correctly understand the priority and show a track of, How Tableau will lead us to Where in the next level.
After finish this tagging exercise then allow ideas to pour in. I think it may be less than a week to cleanup their system. Users can take a Idea Vacation for a week.
Remember this is a temporary halt for ideas sections.