I would like to create a custom field named "Category" to group issues into categories. However categories are evolving over time so I do not want to use a custom field of type enumeration which will have more and more options. Sometimes you might also want to add more than one category.

Instead it would be nice to have a custom field type that works more like tags. That is I simply type in a tag value and a suggestion feature will show me tags I have already used. That custom field should also allow multiple tag values.

Currently the closest workaround is to use a custom field of type text and use contains queries for search. The only downside of text is that you do not see which values/tags have already been used. So when you want to make a query or assign a value/tag to an issue, you need to know all the existing tags because no suggestions can be done by OneDev.