There is a lot of headaches related to currently available feature about either the meaning of the term or how it's implemented and working. What is the meaning of "Ignored"? 🤔 Let take a look here:
Once ignored, the file or folder remains where it is in your Dropbox folder on your computer’s hard drive, but it’s deleted from the Dropbox server and your other devices, can’t be accessed on dropbox.com, and won’t sync to your Dropbox account.
Strange, is the action "delete"-something matching with "ignored"-something? 🤔 I don't think so.
Other consideration: Is "ignore" mean that any change should be ignored completely? Is this mean Dropbox application doesn't observe any change? Also, a change in the cloud might be ignored, if matched local entry gets ignored. 🤔 Is this work so? Rhetorical questions, of course!
About the implementation: How could be ignored a entry (file or directory) which will be available in future or periodically could be removed and reappear again? Attributes only appear on existing files and get gone together with the corresponding file (i.e. no way). In many cases in one directory' tree could be available files, target of sync, and other, usually temporary caches, which have to be ignored. Such case could be extremely difficult to manage. Such situations could appear mostly in development projects, but also a temporary files get "fired" using a text processing applications and other everyday tools. It's very tedious and can engage a huge traffic for meaningless sync (sometimes destructive)!
The solution: Should not be so difficult a filter for files and/or folders to be implemented in the application settings. 😉 Good place could be "Sync" tab in "Dropbox Preferences". Here could be a table, for example, where different types of filtering criteria would be filled. Good criteria could be simple path (either absolute or relative to the Dropbox root), simple file/folder name template (using special symbol, like star-*, for example) or just particular extension, powerfull option could be regular expression, ... and others. Users will fill all needed criteria, as much as needed for every criteria type available. Just noted options are good enough for start. This list could extends over time, according customers needs/queries.
Current try for solution could be left for back compatibility, but is unusable in many cases! That's why - Please, Reconsider it.