The process that I’m using is based around tags and closing the topics.
All suggestions are in a suggestions category, and can be voted on there. When we’re planning to do something, I apply the “planned” tag; when it’s underway, I apply the “underway” tag, and when it’s complete, I apply the “complete” tag. Once an item has been completed, I additionally set the topic to automatically close two weeks later, so that people get their votes back.
To accommodate feedback on completed items, I have a separate “Feature feedback” category. I would dearly love to be able to close off votes without closing off the conversation on the original suggestion, though.
So that all of this works, I’ve customised the look of the specific tags I’m using – “planned” is yellow, “underway” is blue, and “complete” is green. I’ve also tweaked the styling of the vote count for topics you’ve voted on.